diff --git a/esmvalcore/_main.py b/esmvalcore/_main.py
index 9c8d413ef7..5e5668865b 100644
--- a/esmvalcore/_main.py
+++ b/esmvalcore/_main.py
@@ -35,11 +35,15 @@
 import sys
 from importlib.metadata import entry_points
 from pathlib import Path
+from typing import TYPE_CHECKING
 
 import fire
 
 from esmvalcore.config._config import warn_if_old_extra_facets_exist
 
+if TYPE_CHECKING:
+    from esmvalcore.config import Session
+
 # set up logging
 logger = logging.getLogger(__name__)
 
@@ -80,7 +84,7 @@ def parse_resume(resume, recipe):
     return resume
 
 
-def process_recipe(recipe_file: Path, session):
+def process_recipe(recipe_file: Path, session: Session) -> None:
     """Process recipe."""
     import datetime
     import shutil
@@ -318,7 +322,7 @@ def _copy_config_file(
         in_file: Path,
         out_file: Path,
         overwrite: bool,
-    ):
+    ) -> None:
         """Copy a configuration file."""
         import shutil
 
@@ -634,7 +638,7 @@ def _create_session_dir(session):
     def _run(
         self,
         recipe: Path,
-        session,
+        session: Session,
         cli_config_dir: Path | None,
     ) -> None:
         """Run `recipe` using `session`."""
@@ -697,7 +701,7 @@ def _clean_preproc(session):
             shutil.rmtree(session.preproc_dir)
 
     @staticmethod
-    def _get_recipe(recipe) -> Path:
+    def _get_recipe(recipe: str) -> Path:
         from esmvalcore.config._diagnostics import DIAGNOSTICS
 
         if not os.path.isfile(recipe):
diff --git a/esmvalcore/_provenance.py b/esmvalcore/_provenance.py
index a4f3b4c79d..1df4022be2 100644
--- a/esmvalcore/_provenance.py
+++ b/esmvalcore/_provenance.py
@@ -139,7 +139,7 @@ def __init__(
         attributes: dict[str, Any] | None = None,
         ancestors: Iterable[TrackedFile] | None = None,
         prov_filename: str | None = None,
-    ):
+    ) -> None:
         """Create an instance of a file with provenance tracking.
 
         Arguments
@@ -182,7 +182,7 @@ def attributes(self) -> dict[str, Any]:
         return self._attributes
 
     @attributes.setter
-    def attributes(self, value: dict[str, Any] | None):
+    def attributes(self, value: dict[str, Any] | None) -> None:
         """Set attributes describing the file."""
         self._attributes = value
 
@@ -194,11 +194,11 @@ def __repr__(self) -> str:
         """Return representation string (e.g., used by ``pformat``)."""
         return f"{self.__class__.__name__}: {self.filename}"
 
-    def __eq__(self, other) -> bool:
+    def __eq__(self, other: object) -> bool:
         """Check if `other` equals `self`."""
         return hasattr(other, "filename") and self.filename == other.filename
 
-    def __lt__(self, other) -> bool:
+    def __lt__(self, other: object) -> bool:
         """Check if `other` should be sorted before `self`."""
         return hasattr(other, "filename") and self.filename < other.filename
 
diff --git a/esmvalcore/_recipe/check.py b/esmvalcore/_recipe/check.py
index 99e40baff9..55e1b52709 100644
--- a/esmvalcore/_recipe/check.py
+++ b/esmvalcore/_recipe/check.py
@@ -364,7 +364,7 @@ def _verify_span_value(span: str) -> None:
         raise RecipeError(msg)
 
 
-def _verify_groupby(groupby: Any) -> None:
+def _verify_groupby(groupby: list[str]) -> None:
     """Raise error if groupby arguments cannot be verified."""
     if not isinstance(groupby, list):
         msg = (
@@ -375,7 +375,7 @@ def _verify_groupby(groupby: Any) -> None:
         raise RecipeError(msg)
 
 
-def _verify_keep_input_datasets(keep_input_datasets: Any) -> None:
+def _verify_keep_input_datasets(keep_input_datasets: bool) -> None:
     if not isinstance(keep_input_datasets, bool):
         msg = (
             f"Invalid value encountered for `keep_input_datasets`."
@@ -385,7 +385,7 @@ def _verify_keep_input_datasets(keep_input_datasets: Any) -> None:
         raise RecipeError(msg)
 
 
-def _verify_ignore_scalar_coords(ignore_scalar_coords: Any) -> None:
+def _verify_ignore_scalar_coords(ignore_scalar_coords: bool) -> None:
     if not isinstance(ignore_scalar_coords, bool):
         msg = (
             f"Invalid value encountered for `ignore_scalar_coords`."
diff --git a/esmvalcore/_recipe/from_datasets.py b/esmvalcore/_recipe/from_datasets.py
index d0d60e0360..996c81b37a 100644
--- a/esmvalcore/_recipe/from_datasets.py
+++ b/esmvalcore/_recipe/from_datasets.py
@@ -5,7 +5,7 @@
 import itertools
 import logging
 import re
-from collections.abc import Iterable, Mapping, Sequence
+from collections.abc import Iterable, Mapping
 from functools import partial
 from typing import TYPE_CHECKING, Any
 
@@ -16,6 +16,7 @@
 from ._io import _load_recipe
 
 if TYPE_CHECKING:
+    from collections.abc import Sequence
     from pathlib import Path
 
     from esmvalcore.dataset import Dataset
@@ -114,7 +115,7 @@ def _to_frozen(item):
     return item
 
 
-def _move_one_level_up(base: dict, level: str, target: str):
+def _move_one_level_up(base: dict, level: str, target: str) -> None:
     """Move datasets one level up in the recipe."""
     groups = base[level]
     if not groups:
diff --git a/esmvalcore/_recipe/recipe.py b/esmvalcore/_recipe/recipe.py
index da159183ba..4d11956467 100644
--- a/esmvalcore/_recipe/recipe.py
+++ b/esmvalcore/_recipe/recipe.py
@@ -16,7 +16,7 @@
 
 from esmvalcore import __version__, esgf
 from esmvalcore._provenance import get_recipe_provenance
-from esmvalcore._task import BaseTask, DiagnosticTask, ResumeTask, TaskSet
+from esmvalcore._task import DiagnosticTask, ResumeTask, TaskSet
 from esmvalcore.config._config import TASKSEP
 from esmvalcore.config._dask import validate_dask_config
 from esmvalcore.config._diagnostics import TAGS
@@ -59,6 +59,9 @@
 if TYPE_CHECKING:
     from collections.abc import Iterable, Sequence
 
+    from prov.model import ProvEntity
+
+    from esmvalcore._task import BaseTask
     from esmvalcore.config import Session
     from esmvalcore.io.protocol import DataElement
     from esmvalcore.typing import Facets
@@ -964,7 +967,10 @@ def _need_ncl(raw_diagnostics: dict[str, Diagnostic]) -> bool:
                     return True
         return False
 
-    def _initialize_provenance(self, raw_documentation: dict[str, Any]):
+    def _initialize_provenance(
+        self,
+        raw_documentation: dict[str, Any],
+    ) -> ProvEntity:
         """Initialize the recipe provenance."""
         doc = deepcopy(raw_documentation)
 
@@ -1380,10 +1386,10 @@ def write_html_summary(self) -> None:
                 RecipeOutput,
             )
 
-            output = self.get_output()
-
             try:
-                output = RecipeOutput.from_core_recipe_output(output)
+                output = RecipeOutput.from_core_recipe_output(
+                    self.get_output(),
+                )
             except LookupError as error:
                 # See https://github.com/ESMValGroup/ESMValCore/issues/28
                 logger.warning("Could not write HTML report: %s", error)
diff --git a/esmvalcore/_recipe/to_datasets.py b/esmvalcore/_recipe/to_datasets.py
index e335417175..65951450d1 100644
--- a/esmvalcore/_recipe/to_datasets.py
+++ b/esmvalcore/_recipe/to_datasets.py
@@ -3,7 +3,7 @@
 from __future__ import annotations
 
 import logging
-from collections.abc import Iterable, Iterator, Sequence
+from collections.abc import Iterable
 from copy import deepcopy
 from typing import TYPE_CHECKING, Any
 
@@ -23,6 +23,7 @@
 from ._io import _load_recipe
 
 if TYPE_CHECKING:
+    from collections.abc import Iterator, Sequence
     from pathlib import Path
 
     from esmvalcore.config import Session
diff --git a/esmvalcore/_task.py b/esmvalcore/_task.py
index fe77472888..231f119a20 100644
--- a/esmvalcore/_task.py
+++ b/esmvalcore/_task.py
@@ -1,5 +1,7 @@
 """ESMValtool task definition."""
 
+from __future__ import annotations
+
 import abc
 import contextlib
 import datetime
@@ -283,7 +285,7 @@ def flatten(self):
         tasks.add(self)
         return tasks
 
-    def run(self, input_files=None):
+    def run(self, input_files: list[str] | None = None) -> None:
         """Run task."""
         if not self.output_files:
             if input_files is None:
@@ -308,7 +310,7 @@ def run(self, input_files=None):
         return self.output_files
 
     @abc.abstractmethod
-    def _run(self, input_files):
+    def _run(self, input_files: list[str]) -> list[str]:
         """Run task."""
 
     def get_product_attributes(self) -> dict:
@@ -362,7 +364,7 @@ def __init__(self, prev_preproc_dir, preproc_dir, name):
 
         super().__init__(ancestors=None, name=name, products=products)
 
-    def _run(self, _):
+    def _run(self, _: list[str]) -> list[str]:
         """Return the result of a previous run."""
         metadata = self.get_product_attributes()
 
@@ -810,11 +812,11 @@ def available_cpu_count() -> int:
 class TaskSet(set):
     """Container for tasks."""
 
-    def flatten(self) -> "TaskSet":
+    def flatten(self) -> TaskSet:
         """Flatten the list of tasks."""
         return TaskSet(t for task in self for t in task.flatten())
 
-    def get_independent(self) -> "TaskSet":
+    def get_independent(self) -> TaskSet:
         """Return a set of independent tasks."""
         independent_tasks = TaskSet()
         all_tasks = self.flatten()
diff --git a/esmvalcore/cmor/_fixes/cmip5/ec_earth.py b/esmvalcore/cmor/_fixes/cmip5/ec_earth.py
index ef65f1bbba..d892172c95 100644
--- a/esmvalcore/cmor/_fixes/cmip5/ec_earth.py
+++ b/esmvalcore/cmor/_fixes/cmip5/ec_earth.py
@@ -1,6 +1,8 @@
 """Fixes for EC-Earth model."""
 
-from collections.abc import Iterable
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
 
 import iris
 import numpy as np
@@ -12,6 +14,9 @@
     cube_to_aux_coord,
 )
 
+if TYPE_CHECKING:
+    from collections.abc import Iterable
+
 
 class Sic(Fix):
     """Fixes for sic."""
diff --git a/esmvalcore/cmor/_fixes/cmip6/cesm2.py b/esmvalcore/cmor/_fixes/cmip6/cesm2.py
index 4ce856e3de..7279d0aa54 100644
--- a/esmvalcore/cmor/_fixes/cmip6/cesm2.py
+++ b/esmvalcore/cmor/_fixes/cmip6/cesm2.py
@@ -1,7 +1,9 @@
 """Fixes for CESM2 model."""
 
-from pathlib import Path
+from __future__ import annotations
+
 from shutil import copyfile
+from typing import TYPE_CHECKING
 
 import iris
 import iris.coords
@@ -18,6 +20,9 @@
     fix_ocean_depth_coord,
 )
 
+if TYPE_CHECKING:
+    from pathlib import Path
+
 
 class Cl(Fix):
     """Fixes for ``cl``."""
diff --git a/esmvalcore/cmor/_fixes/cmip6/e3sm_1_1.py b/esmvalcore/cmor/_fixes/cmip6/e3sm_1_1.py
index 6918743978..6ba00891eb 100644
--- a/esmvalcore/cmor/_fixes/cmip6/e3sm_1_1.py
+++ b/esmvalcore/cmor/_fixes/cmip6/e3sm_1_1.py
@@ -1,10 +1,15 @@
 """Fixes for E3SM-1-1 model."""
 
-from iris.cube import Cube
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
 
 from esmvalcore.cmor.fix import Fix
 from esmvalcore.preprocessor._shared import get_array_module
 
+if TYPE_CHECKING:
+    from iris.cube import Cube
+
 
 def _mask_greater(cube: Cube, value: float) -> Cube:
     """Mask all data of cube which is greater than ``value``."""
diff --git a/esmvalcore/cmor/_fixes/cmip6/ec_earth3_veg_lr.py b/esmvalcore/cmor/_fixes/cmip6/ec_earth3_veg_lr.py
index fa6ce5e2af..5aafc22cc2 100644
--- a/esmvalcore/cmor/_fixes/cmip6/ec_earth3_veg_lr.py
+++ b/esmvalcore/cmor/_fixes/cmip6/ec_earth3_veg_lr.py
@@ -1,12 +1,17 @@
 """Fixes for EC-Earth3-Veg-LR model."""
 
-from collections.abc import Sequence
+from __future__ import annotations
 
-import iris.cube
+from typing import TYPE_CHECKING
 
 from esmvalcore.cmor._fixes.common import OceanFixGrid
 from esmvalcore.cmor._fixes.fix import Fix
 
+if TYPE_CHECKING:
+    from collections.abc import Sequence
+
+    import iris.cube
+
 
 class AllVars(Fix):
     """Fixes for all variables."""
diff --git a/esmvalcore/cmor/_fixes/fix.py b/esmvalcore/cmor/_fixes/fix.py
index 789724ffe3..388577f33d 100644
--- a/esmvalcore/cmor/_fixes/fix.py
+++ b/esmvalcore/cmor/_fixes/fix.py
@@ -8,13 +8,13 @@
 import logging
 import tempfile
 from pathlib import Path
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Any
 
 import dask
 import numpy as np
 from cf_units import Unit
-from iris.coords import Coord, CoordExtent
-from iris.cube import Cube, CubeList
+from iris.coords import CoordExtent
+from iris.cube import CubeList
 from iris.exceptions import UnitConversionError
 from iris.util import reverse
 
@@ -37,6 +37,8 @@
 
     import ncdata
     import xarray as xr
+    from iris.coords import Coord
+    from iris.cube import Cube
 
     from esmvalcore.cmor.table import CoordinateInfo, VariableInfo
     from esmvalcore.config import Session
@@ -421,12 +423,12 @@ def _msg_suffix(cube: Cube) -> str:
             return f"\n(for file {cube.attributes['source_file']})"
         return f"\n(for variable {cube.var_name})"
 
-    def _debug_msg(self, cube: Cube, msg: str, *args) -> None:
+    def _debug_msg(self, cube: Cube, msg: str, *args: Any) -> None:
         """Print debug message."""
         msg += self._msg_suffix(cube)
         generic_fix_logger.debug(msg, *args)
 
-    def _warning_msg(self, cube: Cube, msg: str, *args) -> None:
+    def _warning_msg(self, cube: Cube, msg: str, *args: Any) -> None:
         """Print debug message."""
         msg += self._msg_suffix(cube)
         generic_fix_logger.warning(msg, *args)
diff --git a/esmvalcore/cmor/_fixes/icon/_base_fixes.py b/esmvalcore/cmor/_fixes/icon/_base_fixes.py
index 4023851862..c94b3483c6 100644
--- a/esmvalcore/cmor/_fixes/icon/_base_fixes.py
+++ b/esmvalcore/cmor/_fixes/icon/_base_fixes.py
@@ -10,7 +10,7 @@
 from pathlib import Path
 from shutil import copyfileobj
 from tempfile import NamedTemporaryFile
-from typing import Any
+from typing import TYPE_CHECKING, Any
 from urllib.parse import urlparse
 
 import iris
@@ -19,8 +19,8 @@
 import requests
 from cf_units import Unit
 from iris import NameConstraint
-from iris.coords import AuxCoord, Coord, DimCoord
-from iris.cube import Cube, CubeList
+from iris.coords import AuxCoord, DimCoord
+from iris.cube import CubeList
 from iris.mesh import Connectivity, MeshXY
 
 import esmvalcore.local
@@ -28,6 +28,10 @@
 from esmvalcore.config._data_sources import _get_data_sources
 from esmvalcore.iris_helpers import add_leading_dim_to_cube, date2num
 
+if TYPE_CHECKING:
+    from iris.coords import Coord
+    from iris.cube import Cube
+
 logger = logging.getLogger(__name__)
 
 
diff --git a/esmvalcore/cmor/_fixes/obs4mips/c3s_gto_ecv_9_0.py b/esmvalcore/cmor/_fixes/obs4mips/c3s_gto_ecv_9_0.py
index 3252ad0745..608e6919fd 100644
--- a/esmvalcore/cmor/_fixes/obs4mips/c3s_gto_ecv_9_0.py
+++ b/esmvalcore/cmor/_fixes/obs4mips/c3s_gto_ecv_9_0.py
@@ -1,10 +1,16 @@
 """Fixes for obs4MIPs dataset C3S-GTO-ECV-9-0."""
 
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
 import dask.array as da
-from iris.cube import Cube
 
 from esmvalcore.cmor._fixes.fix import Fix
 
+if TYPE_CHECKING:
+    from iris.cube import Cube
+
 
 class Toz(Fix):
     """Fixes for toz."""
diff --git a/esmvalcore/cmor/_fixes/shared.py b/esmvalcore/cmor/_fixes/shared.py
index 7cfb832dcf..13d478ea9f 100644
--- a/esmvalcore/cmor/_fixes/shared.py
+++ b/esmvalcore/cmor/_fixes/shared.py
@@ -1,9 +1,12 @@
 """Shared functions for fixes."""
 
+from __future__ import annotations
+
 import logging
 import os
 from datetime import datetime, timedelta
 from functools import cache
+from typing import TYPE_CHECKING
 
 import dask.array as da
 import iris
@@ -11,11 +14,13 @@
 import pandas as pd
 from cf_units import Unit
 from iris import NameConstraint
-from iris.coords import Coord
 from scipy.interpolate import interp1d
 
 from esmvalcore.iris_helpers import date2num
 
+if TYPE_CHECKING:
+    from iris.coords import Coord
+
 logger = logging.getLogger(__name__)
 
 
diff --git a/esmvalcore/cmor/_utils.py b/esmvalcore/cmor/_utils.py
index c88a5b0b4e..da8eddd759 100644
--- a/esmvalcore/cmor/_utils.py
+++ b/esmvalcore/cmor/_utils.py
@@ -5,7 +5,7 @@
 import logging
 from typing import TYPE_CHECKING
 
-from esmvalcore.cmor.table import CMOR_TABLES, CoordinateInfo, VariableInfo
+from esmvalcore.cmor.table import CMOR_TABLES
 
 if TYPE_CHECKING:
     from collections.abc import Sequence
@@ -13,6 +13,8 @@
     from iris.coords import Coord
     from iris.cube import Cube
 
+    from esmvalcore.cmor.table import CoordinateInfo, VariableInfo
+
 logger = logging.getLogger(__name__)
 
 _ALTERNATIVE_GENERIC_LEV_COORDS = {
diff --git a/esmvalcore/cmor/check.py b/esmvalcore/cmor/check.py
index e2d40aa05c..a487eb70ee 100644
--- a/esmvalcore/cmor/check.py
+++ b/esmvalcore/cmor/check.py
@@ -22,7 +22,7 @@
     _get_new_generic_level_coord,
     _get_simplified_calendar,
 )
-from esmvalcore.cmor.table import CoordinateInfo, get_var_info
+from esmvalcore.cmor.table import get_var_info
 from esmvalcore.iris_helpers import has_unstructured_grid
 
 if TYPE_CHECKING:
@@ -31,6 +31,8 @@
     from iris.coords import Coord
     from iris.cube import Cube
 
+    from esmvalcore.cmor.table import CoordinateInfo
+
 
 class CheckLevels(IntEnum):
     """Level of strictness of the checks."""
@@ -540,7 +542,10 @@ def _check_coords(self):
 
         self._check_coord_ranges(coords)
 
-    def _check_coord_ranges(self, coords: list[tuple[CoordinateInfo, Coord]]):
+    def _check_coord_ranges(
+        self,
+        coords: list[tuple[CoordinateInfo, Coord]],
+    ) -> None:
         """Check coordinate value are inside valid ranges."""
 
         class Limit(NamedTuple):
diff --git a/esmvalcore/cmor/fix.py b/esmvalcore/cmor/fix.py
index cbe6aef4b0..4f66ffda25 100644
--- a/esmvalcore/cmor/fix.py
+++ b/esmvalcore/cmor/fix.py
@@ -9,9 +9,9 @@
 
 import logging
 from collections import defaultdict
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Any
 
-from iris.cube import Cube, CubeList
+from iris.cube import CubeList
 
 from esmvalcore.cmor._fixes.fix import Fix
 
@@ -21,6 +21,7 @@
 
     import ncdata
     import xarray as xr
+    from iris.cube import Cube
 
     from esmvalcore.config import Session
 
@@ -37,7 +38,7 @@ def fix_file(  # noqa: PLR0913
     add_unique_suffix: bool = False,
     session: Session | None = None,
     frequency: str | None = None,
-    **extra_facets,
+    **extra_facets: Any,
 ) -> str | Path | xr.Dataset | ncdata.NcData:
     """Fix files before loading them into a :class:`~iris.cube.CubeList`.
 
@@ -120,7 +121,7 @@ def fix_metadata(
     mip: str,
     frequency: str | None = None,
     session: Session | None = None,
-    **extra_facets,
+    **extra_facets: Any,
 ) -> CubeList:
     """Fix cube metadata if fixes are required.
 
@@ -204,7 +205,7 @@ def fix_data(
     mip: str,
     frequency: str | None = None,
     session: Session | None = None,
-    **extra_facets,
+    **extra_facets: Any,
 ) -> Cube:
     """Fix cube data if fixes are required.
 
diff --git a/esmvalcore/config/_config.py b/esmvalcore/config/_config.py
index 121ee2b126..565ea4a6d4 100644
--- a/esmvalcore/config/_config.py
+++ b/esmvalcore/config/_config.py
@@ -94,7 +94,7 @@ def warn_if_old_extra_facets_exist() -> None:
         )
 
 
-def load_config_developer(cfg_file) -> dict:
+def load_config_developer(cfg_file: Path) -> dict:
     """Read the developer's configuration file."""
     with open(cfg_file, encoding="utf-8") as file:
         cfg = yaml.safe_load(file)
diff --git a/esmvalcore/config/_config_object.py b/esmvalcore/config/_config_object.py
index fcdddc9c37..d03c8409b6 100644
--- a/esmvalcore/config/_config_object.py
+++ b/esmvalcore/config/_config_object.py
@@ -276,7 +276,7 @@ class Session(ValidatedConfig):
     relative_cmor_log = Path("run", "cmor_log.txt")
     _relative_fixed_file_dir = Path("preproc", "fixed_files")
 
-    def __init__(self, config: dict, name: str = "session"):
+    def __init__(self, config: dict, name: str = "session") -> None:
         super().__init__(config)
         self.session_name: str | None = None
         self.set_session_name(name)
@@ -293,7 +293,7 @@ def __repr__(self) -> str:
     def __str__(self) -> str:
         return repr(self)
 
-    def set_session_name(self, name: str = "session"):
+    def set_session_name(self, name: str = "session") -> None:
         """Set the name for the session.
 
         The `name` is used to name the session directory, e.g.
diff --git a/esmvalcore/config/_config_validators.py b/esmvalcore/config/_config_validators.py
index efb5e2538f..ca5045f976 100644
--- a/esmvalcore/config/_config_validators.py
+++ b/esmvalcore/config/_config_validators.py
@@ -5,11 +5,11 @@
 import logging
 import os.path
 import warnings
-from collections.abc import Callable, Iterable
+from collections.abc import Iterable
 from functools import lru_cache, partial
 from importlib.resources import files as importlib_files
 from pathlib import Path
-from typing import TYPE_CHECKING, Any
+from typing import TYPE_CHECKING, Any, Literal
 
 from packaging import version
 
@@ -22,6 +22,8 @@
 )
 
 if TYPE_CHECKING:
+    from collections.abc import Callable
+
     from esmvalcore.config._validated_config import ValidatedConfig
 
 logger = logging.getLogger(__name__)
@@ -47,7 +49,11 @@ class ValidationError(ValueError):
 # to fit the needs of ESMValCore. Matplotlib is licenced under the terms of
 # the the 'Python Software Foundation License'
 # (https://www.python.org/psf/license)
-def _make_type_validator(cls: Any, *, allow_none: bool = False) -> Any:
+def _make_type_validator(
+    cls: Any,  # noqa: ANN401
+    *,
+    allow_none: bool = False,
+) -> Callable:
     """Construct a type validator for `cls`.
 
     Return a validator that converts inputs to *cls* or raises (and
@@ -361,7 +367,9 @@ def validate_extra_facets_dir(value):
     return validate_pathlist(value)
 
 
-def validate_projects(value: Any) -> Any:
+def validate_projects(
+    value: dict,
+) -> dict[str, dict[str, Any]]:
     """Validate projects mapping."""
     mapping = validate_dict(value)
     options_for_project: dict[str, Callable[[Any], Any]] = {
@@ -444,8 +452,8 @@ def _handle_deprecation(
 # TODO: remove in v2.15.0
 def deprecate_extra_facets_dir(
     validated_config: ValidatedConfig,
-    value: Any,
-    validated_value: Any,
+    value: str | Path,
+    validated_value: str | Path,
 ) -> None:
     """Deprecate ``extra_facets_dir`` option.
 
@@ -481,8 +489,8 @@ def deprecate_extra_facets_dir(
 
 def deprecate_rootpath(
     validated_config: ValidatedConfig,
-    value: Any,
-    validated_value: Any,
+    value: dict,
+    validated_value: dict,
 ) -> None:
     """Deprecate ``rootpath`` option.
 
@@ -508,8 +516,8 @@ def deprecate_rootpath(
 
 def deprecate_drs(
     validated_config: ValidatedConfig,  # noqa: ARG001
-    value: Any,  # noqa: ARG001
-    validated_value: Any,  # noqa: ARG001
+    value: dict,  # noqa: ARG001
+    validated_value: dict,  # noqa: ARG001
 ) -> None:
     """Deprecate ``drs`` option.
 
@@ -529,8 +537,8 @@ def deprecate_drs(
 
 def deprecate_download_dir(
     validated_config: ValidatedConfig,  # noqa: ARG001
-    value: Any,  # noqa: ARG001
-    validated_value: Any,  # noqa: ARG001
+    value: str | Path,  # noqa: ARG001
+    validated_value: str | Path,  # noqa: ARG001
 ) -> None:
     """Deprecate ``download_dir`` option.
 
@@ -550,8 +558,8 @@ def deprecate_download_dir(
 
 def deprecate_search_esgf(
     validated_config: ValidatedConfig,
-    value: Any,  # noqa: ARG001
-    validated_value: Any,
+    value: Literal["never", "when_missing", "always"],  # noqa: ARG001
+    validated_value: Literal["never", "when_missing", "always"],
 ) -> None:
     """Deprecate ``search_esgf`` option.
 
diff --git a/esmvalcore/config/_dask.py b/esmvalcore/config/_dask.py
index 6ffed159c4..10c2195101 100644
--- a/esmvalcore/config/_dask.py
+++ b/esmvalcore/config/_dask.py
@@ -1,9 +1,11 @@
 """Configuration for Dask distributed."""
 
+from __future__ import annotations
+
 import contextlib
 import importlib
 import logging
-from collections.abc import Generator, Mapping
+from collections.abc import Mapping
 from copy import deepcopy
 from typing import TYPE_CHECKING
 
@@ -16,6 +18,8 @@
 )
 
 if TYPE_CHECKING:
+    from collections.abc import Generator
+
     from distributed.deploy import Cluster
 
 logger = logging.getLogger(__name__)
diff --git a/esmvalcore/config/_data_sources.py b/esmvalcore/config/_data_sources.py
index 903ae7c5bf..d4f8ad80c3 100644
--- a/esmvalcore/config/_data_sources.py
+++ b/esmvalcore/config/_data_sources.py
@@ -1,16 +1,21 @@
 """Module for configuring data sources."""
 
+from __future__ import annotations
+
 import logging
+from typing import TYPE_CHECKING
 
 import yaml
 
 import esmvalcore.esgf
 import esmvalcore.esgf.facets
 import esmvalcore.local
-from esmvalcore.config import Session
 from esmvalcore.exceptions import InvalidConfigParameter, RecipeError
 from esmvalcore.io import load_data_sources
-from esmvalcore.io.protocol import DataSource
+
+if TYPE_CHECKING:
+    from esmvalcore.config import Session
+    from esmvalcore.io.protocol import DataSource
 
 logger = logging.getLogger(__name__)
 
diff --git a/esmvalcore/config/_diagnostics.py b/esmvalcore/config/_diagnostics.py
index 16a5d7cfc9..53ee975f94 100644
--- a/esmvalcore/config/_diagnostics.py
+++ b/esmvalcore/config/_diagnostics.py
@@ -3,6 +3,7 @@
 import logging
 import os
 from pathlib import Path
+from typing import Self
 
 import yaml
 
@@ -80,7 +81,7 @@ def __init__(self, *args, **kwargs):
         self.source_file = None
 
     @classmethod
-    def from_file(cls, filename: str):
+    def from_file(cls, filename: str) -> Self:
         """Load the reference tags used for provenance recording."""
         if os.path.exists(filename):
             logger.debug("Loading tags from %s", filename)
@@ -93,7 +94,7 @@ def from_file(cls, filename: str):
             logger.debug("No tags loaded, file %s not present", filename)
             return cls()
 
-    def set_tag_value(self, section: str, tag: str, value):
+    def set_tag_value(self, section: str, tag: str, value: str) -> None:
         """Set the value of a tag in a section.
 
         Parameters
@@ -110,7 +111,7 @@ def set_tag_value(self, section: str, tag: str, value):
 
         self[section][tag] = value
 
-    def set_tag_values(self, tag_values: dict):
+    def set_tag_values(self, tag_values: dict[str, dict[str, str]]) -> None:
         """Update tags from dict.
 
         Parameters
@@ -122,7 +123,7 @@ def set_tag_values(self, tag_values: dict):
             for tag, value in tags.items():
                 self.set_tag_value(section, tag, value)
 
-    def get_tag_value(self, section: str, tag: str):
+    def get_tag_value(self, section: str, tag: str) -> str:
         """Retrieve the value of a tag from a section.
 
         Parameters
@@ -140,25 +141,23 @@ def get_tag_value(self, section: str, tag: str):
         if tag not in self[section]:
             postfix = f" of {self.source_file}" if self.source_file else ""
             msg = f"Tag '{tag}' does not exist in section '{section}'{postfix}"
-            raise ValueError(
-                msg,
-            )
+            raise ValueError(msg)
 
         return self[section][tag]
 
-    def get_tag_values(self, section: str, tags: tuple):
+    def get_tag_values(self, section: str, tags: tuple) -> tuple[str, ...]:
         """Retrieve the values for a list of tags from a section.
 
         Parameters
         ----------
-        section : str
+        section
             Name of the subsection
-        tags : tuple[str] or list[str]
-            List or tuple with tag names
+        tags
+            Tuple with tag names
         """
         return tuple(self.get_tag_value(section, tag) for tag in tags)
 
-    def replace_tags_in_dict(self, dct: dict):
+    def replace_tags_in_dict(self, dct: dict) -> None:
         """Resolve tags and updates the given dict in-place.
 
         Tags are updated one level deep, and only if the corresponding
diff --git a/esmvalcore/config/_logging.py b/esmvalcore/config/_logging.py
index 89d1d59851..9332c133f2 100644
--- a/esmvalcore/config/_logging.py
+++ b/esmvalcore/config/_logging.py
@@ -1,18 +1,22 @@
 """Configure logging."""
 
+from __future__ import annotations
+
 import inspect
 import logging
 import logging.config
 import os
 import time
-from collections.abc import Iterable
 from pathlib import Path
-from typing import Literal
+from typing import TYPE_CHECKING, Literal
 
 import yaml
 
 import esmvalcore.exceptions
 
+if TYPE_CHECKING:
+    from collections.abc import Iterable
+
 _WARNINGS_SHOWN_IN_MAIN_LOG = [
     cls.__name__
     for cls in vars(esmvalcore.exceptions).values()
@@ -96,7 +100,7 @@ def _get_log_files(
     return log_files
 
 
-def _update_stream_level(cfg: dict, level=None):
+def _update_stream_level(cfg: dict, level: str | None = None) -> None:
     """Update the log level for the stream handlers."""
     handlers = cfg["handlers"]
 
diff --git a/esmvalcore/config/_validated_config.py b/esmvalcore/config/_validated_config.py
index 624068c411..65d42cc5e7 100644
--- a/esmvalcore/config/_validated_config.py
+++ b/esmvalcore/config/_validated_config.py
@@ -4,10 +4,10 @@
 
 import pprint
 import warnings
-from collections.abc import Callable, Generator, Mapping, MutableMapping
+from collections.abc import MutableMapping
 from contextlib import contextmanager
 from copy import deepcopy
-from typing import Any, ClassVar
+from typing import TYPE_CHECKING, Any, ClassVar
 
 from esmvalcore.exceptions import (
     InvalidConfigParameter,
@@ -16,6 +16,9 @@
 
 from ._config_validators import ValidationError
 
+if TYPE_CHECKING:
+    from collections.abc import Callable, Generator, Mapping
+
 
 # The code for this class was take from matplotlib (v3.3) and modified to
 # fit the needs of ESMValCore. Matplotlib is licenced under the terms of
@@ -57,7 +60,7 @@ class ValidatedConfig(MutableMapping):
     """
 
     # validate values on the way in
-    def __init__(self, *args, **kwargs) -> None:
+    def __init__(self, *args, **kwargs):
         super().__init__()
         self._mapping: dict[str, Any] = {}
         self.update(*args, **kwargs)
diff --git a/esmvalcore/dataset.py b/esmvalcore/dataset.py
index 157bd69bb6..5c799d0843 100644
--- a/esmvalcore/dataset.py
+++ b/esmvalcore/dataset.py
@@ -19,7 +19,7 @@
 from esmvalcore._recipe import check
 from esmvalcore._recipe.from_datasets import datasets_to_recipe
 from esmvalcore.cmor.table import _get_mips, _update_cmor_facets
-from esmvalcore.config import CFG, Session
+from esmvalcore.config import CFG
 from esmvalcore.config._config import (
     get_activity,
     get_institutes,
@@ -27,10 +27,7 @@
 )
 from esmvalcore.config._data_sources import _get_data_sources
 from esmvalcore.exceptions import InputFilesNotFound, RecipeError
-from esmvalcore.local import (
-    _dates_to_timerange,
-    _get_output_file,
-)
+from esmvalcore.local import _dates_to_timerange, _get_output_file
 from esmvalcore.preprocessor import preprocess
 
 if TYPE_CHECKING:
@@ -38,6 +35,7 @@
 
     from iris.cube import Cube
 
+    from esmvalcore.config import Session
     from esmvalcore.io.protocol import DataElement, DataSource
     from esmvalcore.preprocessor import PreprocessorItem
     from esmvalcore.typing import Facets, FacetValue
@@ -673,7 +671,7 @@ def augment_facets(self) -> None:
             supplementary._augment_facets()  # noqa: SLF001
 
     @staticmethod
-    def _pattern_filter(patterns: Iterable[str], name) -> list[str]:
+    def _pattern_filter(patterns: Iterable[str], name: str) -> list[str]:
         """Get the subset of the list `patterns` that `name` matches."""
         return [pat for pat in patterns if fnmatch.fnmatchcase(name, pat)]
 
@@ -686,16 +684,16 @@ def _get_extra_facets(self) -> dict[str, Any]:
             .get(self["project"], {})
             .get("extra_facets", {})
         )
-        dataset_names = self._pattern_filter(raw_extra_facets, self["dataset"])
+        dataset_names = self._pattern_filter(raw_extra_facets, self["dataset"])  # type: ignore[arg-type]
         for dataset_name in dataset_names:
             mips = self._pattern_filter(
                 raw_extra_facets[dataset_name],
-                self["mip"],
+                self["mip"],  # type: ignore[arg-type]
             )
             for mip in mips:
                 variables = self._pattern_filter(
                     raw_extra_facets[dataset_name][mip],
-                    self["short_name"],
+                    self["short_name"],  # type: ignore[arg-type]
                 )
                 for var in variables:
                     facets = raw_extra_facets[dataset_name][mip][var]
@@ -709,16 +707,16 @@ def _get_extra_facets(self) -> dict[str, Any]:
             self.facets["project"],
             tuple(self.session["extra_facets_dir"]),
         )
-        dataset_names = self._pattern_filter(project_details, self["dataset"])
+        dataset_names = self._pattern_filter(project_details, self["dataset"])  # type: ignore[arg-type]
         for dataset_name in dataset_names:
             mips = self._pattern_filter(
                 project_details[dataset_name],
-                self["mip"],
+                self["mip"],  # type: ignore[arg-type]
             )
             for mip in mips:
                 variables = self._pattern_filter(
                     project_details[dataset_name][mip],
-                    self["short_name"],
+                    self["short_name"],  # type: ignore[arg-type]
                 )
                 for var in variables:
                     facets = project_details[dataset_name][mip][var]
@@ -927,7 +925,7 @@ def _expand_range(self, input_tag: str) -> list[FacetValue]:
         expanded: list[FacetValue] = []
         regex = re.compile(r"\(\d+:\d+\)")
 
-        def expand_range(input_range) -> None:
+        def expand_range(input_range: str) -> None:
             match = regex.search(input_range)
             if match:
                 start, end = match.group(0)[1:-1].split(":")
@@ -948,7 +946,7 @@ def expand_range(input_range) -> None:
                     raise RecipeError(msg)
             expanded.append(tag)
         else:
-            expand_range(tag)
+            expand_range(tag)  # type: ignore[arg-type]
 
         return expanded
 
diff --git a/esmvalcore/esgf/_download.py b/esmvalcore/esgf/_download.py
index ce5f030735..bb565963b9 100644
--- a/esmvalcore/esgf/_download.py
+++ b/esmvalcore/esgf/_download.py
@@ -37,7 +37,7 @@
     from collections.abc import Iterable
 
     import iris.cube
-    from pyesgf.search.results import FileResult
+    from pyesgf.search.results import FileResult, ResultSet
 
     from esmvalcore.typing import Facets
 
@@ -331,7 +331,7 @@ def _get_facets(self, results):
         return facets
 
     @staticmethod
-    def _get_facets_from_dataset_id(results) -> Facets:
+    def _get_facets_from_dataset_id(results: ResultSet) -> Facets:
         """Read the facets from the `dataset_id`."""
         # This reads the facets from the dataset_id because the facets
         # provided by ESGF are unreliable.
@@ -610,7 +610,7 @@ def download(files, dest_folder=None, n_jobs=4):
     files = sorted(files)
     logger.info(get_download_message(files))
 
-    def _download(file: ESGFFile):
+    def _download(file: ESGFFile) -> None:
         """Download file to dest_folder."""
         file.download(dest_folder)
 
diff --git a/esmvalcore/experimental/_logging.py b/esmvalcore/experimental/_logging.py
index 00201909fc..d983cd37c4 100644
--- a/esmvalcore/experimental/_logging.py
+++ b/esmvalcore/experimental/_logging.py
@@ -1,12 +1,18 @@
 """Logging utilities."""
 
+from __future__ import annotations
+
 import logging
 from contextlib import contextmanager
-from pathlib import Path
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from contextlib.abc import ContextManager
+    from pathlib import Path
 
 
 @contextmanager
-def log_to_dir(drc: Path):
+def log_to_dir(drc: Path) -> ContextManager[None]:
     """Log messages to the specified directory.
 
     This is a context manager to temporarily redirect the logging when
diff --git a/esmvalcore/experimental/recipe.py b/esmvalcore/experimental/recipe.py
index 9bb4f513cc..1da67e9ce1 100644
--- a/esmvalcore/experimental/recipe.py
+++ b/esmvalcore/experimental/recipe.py
@@ -1,20 +1,27 @@
 """Recipe metadata."""
 
+from __future__ import annotations
+
 import logging
-import os
 import pprint
 import shutil
 from pathlib import Path
+from typing import TYPE_CHECKING
 
 import yaml
 
 from esmvalcore._recipe.recipe import Recipe as RecipeEngine
-from esmvalcore.config import CFG, Session
+from esmvalcore.config import CFG
 
 from ._logging import log_to_dir
 from .recipe_info import RecipeInfo
 from .recipe_output import RecipeOutput
 
+if TYPE_CHECKING:
+    import os
+
+    from esmvalcore.config import Session
+
 logger = logging.getLogger(__name__)
 
 
@@ -29,7 +36,7 @@ class Recipe:
         Path to the recipe.
     """
 
-    def __init__(self, path: os.PathLike):
+    def __init__(self, path: os.PathLike) -> None:
         self.path = Path(path)
         if not self.path.exists():
             msg = f"Cannot find recipe: `{path}`."
@@ -104,7 +111,7 @@ def run(
         self,
         task: str | None = None,
         session: Session | None = None,
-    ):
+    ) -> RecipeOutput:
         """Run the recipe.
 
         This function loads the recipe into the ESMValCore recipe format
@@ -112,17 +119,17 @@ def run(
 
         Parameters
         ----------
-        task : str
+        task
             Specify the name of the diagnostic or preprocessor to run a
             single task.
-        session : :obj:`Session`, optional
+        session
             Defines the config parameters and location where the recipe
             output will be stored. If ``None``, a new session will be
             started automatically.
 
         Returns
         -------
-        output : dict
+        :
             Returns output of the recipe as instances of :obj:`OutputItem`
             grouped by diagnostic task.
         """
@@ -150,7 +157,7 @@ def get_output(self) -> RecipeOutput:
 
         Returns
         -------
-        output : dict
+        output
             Returns output of the recipe as instances of :obj:`OutputFile`
             grouped by diagnostic task.
         """
@@ -163,6 +170,6 @@ def get_output(self) -> RecipeOutput:
 
         return RecipeOutput(
             task_output=task_output,
-            session=self.last_session,
+            session=self.last_session,  # type: ignore[arg-type]
             info=self.info,
         )
diff --git a/esmvalcore/experimental/recipe_info.py b/esmvalcore/experimental/recipe_info.py
index 1831d16dd8..e2c61edbe2 100644
--- a/esmvalcore/experimental/recipe_info.py
+++ b/esmvalcore/experimental/recipe_info.py
@@ -1,13 +1,22 @@
 """Handles recipe metadata (under 'documentation' section)."""
 
-import os
+from __future__ import annotations
+
 import textwrap
 from pathlib import Path
+from typing import TYPE_CHECKING, Any, Self
 
 import yaml
 
-from .recipe_metadata import Contributor, Project, Reference
-from .templates import get_template
+from esmvalcore.experimental.recipe_metadata import (
+    Contributor,
+    Project,
+    Reference,
+)
+from esmvalcore.experimental.templates import get_template
+
+if TYPE_CHECKING:
+    import os
 
 
 class RecipeInfo:
@@ -21,7 +30,11 @@ class RecipeInfo:
         Name of recipe file
     """
 
-    def __init__(self, data, filename: os.PathLike | str):
+    def __init__(
+        self,
+        data: dict[str, Any],
+        filename: os.PathLike | str,
+    ) -> None:
         self.filename = Path(filename).name
         self.data = data
         self._authors: tuple[Contributor, ...] | None = None
@@ -70,7 +83,7 @@ def _repr_html_(self) -> str:
         return self.render()
 
     @classmethod
-    def from_yaml(cls, path: str):
+    def from_yaml(cls, path: str) -> Self:
         """Return instance of 'RecipeInfo' from a recipe in yaml format."""
         data = yaml.safe_load(Path(path).read_text(encoding="utf-8"))
         return cls(data, filename=path)
diff --git a/esmvalcore/experimental/recipe_metadata.py b/esmvalcore/experimental/recipe_metadata.py
index 6021d8ccf3..f674d33d49 100644
--- a/esmvalcore/experimental/recipe_metadata.py
+++ b/esmvalcore/experimental/recipe_metadata.py
@@ -1,5 +1,7 @@
 """API for recipe metadata."""
 
+from __future__ import annotations
+
 import pybtex
 from pybtex.database.input import bibtex
 
@@ -23,7 +25,12 @@ class Contributor:
         ORCID url
     """
 
-    def __init__(self, name: str, institute: str, orcid: str | None = None):
+    def __init__(
+        self,
+        name: str,
+        institute: str,
+        orcid: str | None = None,
+    ) -> None:
         self.name = name
         self.institute = institute
         self.orcid = orcid
@@ -48,7 +55,7 @@ def _repr_markdown_(self) -> str:
         return str(self)
 
     @classmethod
-    def from_tag(cls, tag: str) -> "Contributor":
+    def from_tag(cls, tag: str) -> Contributor:
         """Return an instance of Contributor from a tag (``TAGS``).
 
         Parameters
@@ -89,7 +96,7 @@ class Project:
         The project title.
     """
 
-    def __init__(self, project: str):
+    def __init__(self, project: str) -> None:
         self.project = project
 
     def __repr__(self) -> str:
@@ -101,7 +108,7 @@ def __str__(self) -> str:
         return f"{self.project}"
 
     @classmethod
-    def from_tag(cls, tag: str) -> "Project":
+    def from_tag(cls, tag: str) -> Project:
         """Return an instance of Project from a tag (``TAGS``).
 
         Parameters
@@ -127,7 +134,7 @@ class Reference:
         If the bibtex file contains more than 1 entry.
     """
 
-    def __init__(self, filename: str):
+    def __init__(self, filename: str) -> None:
         parser = bibtex.Parser(strict=False)
         bib_data = parser.parse_file(filename)
 
@@ -145,7 +152,7 @@ def __init__(self, filename: str):
         self._filename = filename
 
     @classmethod
-    def from_tag(cls, tag: str) -> "Reference":
+    def from_tag(cls, tag: str) -> Reference:
         """Return an instance of Reference from a bibtex tag.
 
         Parameters
diff --git a/esmvalcore/experimental/recipe_output.py b/esmvalcore/experimental/recipe_output.py
index caffe01818..d70902ba7a 100644
--- a/esmvalcore/experimental/recipe_output.py
+++ b/esmvalcore/experimental/recipe_output.py
@@ -1,5 +1,7 @@
 """API for handing recipe output."""
 
+from __future__ import annotations
+
 import base64
 import getpass
 import logging
@@ -7,15 +9,19 @@
 import sys
 from collections.abc import Mapping, Sequence
 from pathlib import Path
+from typing import TYPE_CHECKING, Any, Self
 
 import iris
 import xarray as xr
 
 from esmvalcore.config._config import TASKSEP
+from esmvalcore.experimental.recipe_info import RecipeInfo
+from esmvalcore.experimental.recipe_metadata import Contributor, Reference
+from esmvalcore.experimental.templates import get_template
 
-from .recipe_info import RecipeInfo
-from .recipe_metadata import Contributor, Reference
-from .templates import get_template
+if TYPE_CHECKING:
+    import esmvalcore._task
+    import esmvalcore.config
 
 logger = logging.getLogger(__name__)
 
@@ -31,7 +37,7 @@ class TaskOutput:
         Mapping of the filenames with the associated attributes.
     """
 
-    def __init__(self, name: str, files: dict):
+    def __init__(self, name: str, files: dict) -> None:
         self.name = name
         self.title = name.replace("_", " ").replace(TASKSEP, ": ").title()
         self.files = tuple(
@@ -55,7 +61,7 @@ def __len__(self):
         """Return number of files."""
         return len(self.files)
 
-    def __getitem__(self, index: int):
+    def __getitem__(self, index: int) -> OutputFile:
         """Get item indexed by `index`."""
         return self.files[index]
 
@@ -70,11 +76,8 @@ def data_files(self) -> tuple:
         return tuple(item for item in self.files if item.kind == "data")
 
     @classmethod
-    def from_task(cls, task) -> "TaskOutput":
-        """Create an instance of `TaskOutput` from a Task.
-
-        Where task is an instance of `esmvalcore._task.BaseTask`.
-        """
+    def from_task(cls, task: esmvalcore._task.BaseTask) -> TaskOutput:
+        """Create an instance of `TaskOutput` from a Task."""
         product_attributes = task.get_product_attributes()
         return cls(name=task.name, files=product_attributes)
 
@@ -114,18 +117,18 @@ class RecipeOutput(Mapping):
 
     Parameters
     ----------
-    task_output : dict
+    task_output
         Dictionary with recipe output grouped by task name. Each task value is
         a mapping of the filenames with the product attributes.
 
     Attributes
     ----------
-    diagnostics : dict
+    diagnostics
         Dictionary with recipe output grouped by diagnostic.
-    info : RecipeInfo
-        The recipe used to create the output.
-    session : esmvalcore.config.Session
+    session
         The session used to run the recipe.
+    info
+        The recipe used to create the output.
     """
 
     FILTER_ATTRS: tuple = (
@@ -135,7 +138,12 @@ class RecipeOutput(Mapping):
         "long_names",
     )
 
-    def __init__(self, task_output: dict, session=None, info=None):
+    def __init__(
+        self,
+        task_output: dict[str, dict[str, Any]],
+        session: esmvalcore.config.Session,
+        info: RecipeInfo,
+    ) -> None:
         self._raw_task_output = task_output
         self._task_output = {}
         self.diagnostics = {}
@@ -197,7 +205,7 @@ def __repr__(self):
         """Return canonical string representation."""
         return "\n".join(repr(item) for item in self._task_output.values())
 
-    def __getitem__(self, key: str):
+    def __getitem__(self, key: str) -> TaskOutput:
         """Get task indexed by `key`."""
         return self._task_output[key]
 
@@ -210,8 +218,8 @@ def __len__(self):
         return len(self._task_output)
 
     @classmethod
-    def from_core_recipe_output(cls, recipe_output: dict):
-        """Construct instance from `_recipe.Recipe` output.
+    def from_core_recipe_output(cls, recipe_output: dict) -> Self:
+        """Construct instance from `esmvalcore._recipe.recipe.Recipe.get_output`.
 
         The core recipe format is not directly compatible with the API. This
         constructor converts the raw recipe dict to :obj:`RecipeInfo`
@@ -219,7 +227,7 @@ def from_core_recipe_output(cls, recipe_output: dict):
         Parameters
         ----------
         recipe_output : dict
-            Output from `_recipe.Recipe.get_product_output`
+            Output from `esmvalcore._recipe.recipe.Recipe.get_output`
         """
         task_output = recipe_output["task_output"]
         recipe_data = recipe_output["recipe_data"]
@@ -321,7 +329,7 @@ class OutputFile:
 
     kind: str | None = None
 
-    def __init__(self, path: str, attributes: dict | None = None):
+    def __init__(self, path: str, attributes: dict | None = None) -> None:
         if not attributes:
             attributes = {}
 
@@ -358,14 +366,18 @@ def references(self) -> tuple:
             self._references = tuple(Reference.from_tag(tag) for tag in tags)
         return self._references
 
-    def _get_derived_path(self, append: str, suffix: str | None = None):
+    def _get_derived_path(
+        self,
+        append: str,
+        suffix: str | None = None,
+    ) -> Path:
         """Return path of related files.
 
         Parameters
         ----------
-        append : str
+        append
             Add this string to the stem of the path.
-        suffix : str
+        suffix
             The file extension to use (i.e. `.txt`)
 
         Returns
@@ -396,7 +408,7 @@ def create(
         cls,
         path: str,
         attributes: dict | None = None,
-    ) -> "OutputFile":
+    ) -> OutputFile:
         """Construct new instances of OutputFile.
 
         Chooses a derived class if suitable.
diff --git a/esmvalcore/experimental/utils.py b/esmvalcore/experimental/utils.py
index c24525f110..dc2ba5dea5 100644
--- a/esmvalcore/experimental/utils.py
+++ b/esmvalcore/experimental/utils.py
@@ -1,19 +1,23 @@
 """ESMValCore utilities."""
 
-import os
+from __future__ import annotations
+
 import re
 from pathlib import Path
-from re import Pattern
+from typing import TYPE_CHECKING
 
 from esmvalcore.config._diagnostics import DIAGNOSTICS
+from esmvalcore.experimental.recipe import Recipe
 
-from .recipe import Recipe
+if TYPE_CHECKING:
+    import os
+    from re import Pattern
 
 
 class RecipeList(list):
     """Container for recipes."""
 
-    def find(self, query: Pattern[str]):
+    def find(self, query: Pattern[str]) -> RecipeList:
         """Search for recipes matching the search query or pattern.
 
         Searches in the description, authors and project information fields.
diff --git a/esmvalcore/io/__init__.py b/esmvalcore/io/__init__.py
index 13022f8bf1..ef6e056282 100644
--- a/esmvalcore/io/__init__.py
+++ b/esmvalcore/io/__init__.py
@@ -44,11 +44,16 @@
 :attr:`esmvalcore.io.protocol.DataSource.priority` is chosen.
 """
 
+from __future__ import annotations
+
 import importlib
 import logging
+from typing import TYPE_CHECKING
+
+import esmvalcore.io.protocol
 
-from esmvalcore.config import Session
-from esmvalcore.io.protocol import DataSource
+if TYPE_CHECKING:
+    from esmvalcore.config import Session
 
 logger = logging.getLogger(__name__)
 
@@ -56,7 +61,7 @@
 def load_data_sources(
     session: Session,
     project: str | None = None,
-) -> list[DataSource]:
+) -> list[esmvalcore.io.protocol.DataSource]:
     """Get the list of available data sources.
 
     If no ``priority`` is configured for a data source, the default priority
@@ -71,7 +76,7 @@ def load_data_sources(
 
     Returns
     -------
-    :obj:`list` of :obj:`DataSource`:
+    :
         A list of available data sources.
 
     Raises
@@ -80,7 +85,7 @@ def load_data_sources(
         If the project or its settings are not found in the configuration.
 
     """
-    data_sources: list[DataSource] = []
+    data_sources: list[esmvalcore.io.protocol.DataSource] = []
     if project is not None and project not in session["projects"]:
         msg = f"Unknown project '{project}', please configure it under 'projects'."
         raise ValueError(msg)
@@ -102,7 +107,7 @@ def load_data_sources(
                 priority=priority,
                 **kwargs,
             )
-            if not isinstance(data_source, DataSource):
+            if not isinstance(data_source, esmvalcore.io.protocol.DataSource):
                 msg = (
                     "Expected a data source of type `esmvalcore.io.protocol.DataSource`, "
                     f"but your configuration for project '{project_}' contains "
diff --git a/esmvalcore/io/protocol.py b/esmvalcore/io/protocol.py
index 6f7108c2a7..37239eef89 100644
--- a/esmvalcore/io/protocol.py
+++ b/esmvalcore/io/protocol.py
@@ -11,12 +11,16 @@
 
 """
 
-from collections.abc import Iterable
-from typing import Any, Protocol, runtime_checkable
+from __future__ import annotations
 
-import iris.cube
+from typing import TYPE_CHECKING, Any, Protocol, runtime_checkable
 
-from esmvalcore.typing import FacetValue
+if TYPE_CHECKING:
+    from collections.abc import Iterable
+
+    import iris.cube
+
+    from esmvalcore.typing import FacetValue
 
 
 @runtime_checkable
diff --git a/esmvalcore/iris_helpers.py b/esmvalcore/iris_helpers.py
index 451720baf8..dfba3ca503 100644
--- a/esmvalcore/iris_helpers.py
+++ b/esmvalcore/iris_helpers.py
@@ -575,7 +575,7 @@ def ignore_warnings_context(
 def _get_attribute(
     data: ncdata.NcData | ncdata.NcVariable | xr.Dataset | xr.DataArray,
     attribute_name: str,
-) -> Any:
+) -> Any:  # noqa: ANN401
     """Get attribute from an ncdata or xarray object."""
     if isinstance(data, ncdata.NcData | ncdata.NcVariable):
         attribute = data.attributes[attribute_name].value
diff --git a/esmvalcore/local.py b/esmvalcore/local.py
index 2f8ace30db..bb0b2049f1 100644
--- a/esmvalcore/local.py
+++ b/esmvalcore/local.py
@@ -56,7 +56,7 @@
 import iris.fileformats.cf
 import isodate
 from cf_units import Unit
-from netCDF4 import Dataset, Variable
+from netCDF4 import Dataset
 
 import esmvalcore.io.protocol
 from esmvalcore.config import CFG
@@ -67,6 +67,8 @@
 if TYPE_CHECKING:
     from collections.abc import Iterable
 
+    from netCDF4 import Variable
+
     from esmvalcore.typing import Facets, FacetValue
 
 logger = logging.getLogger(__name__)
@@ -551,7 +553,7 @@ def __post_init__(self) -> None:
         self.rootpath = Path(os.path.expandvars(self.rootpath)).expanduser()
         self._regex_pattern = self._templates_to_regex()
 
-    def _get_glob_patterns(self, **facets) -> list[Path]:
+    def _get_glob_patterns(self, **facets: FacetValue) -> list[Path]:
         """Compose the globs that will be used to look for files."""
         dirname_globs = _replace_tags(self.dirname_template, facets)
         filename_globs = _replace_tags(self.filename_template, facets)
@@ -561,7 +563,7 @@ def _get_glob_patterns(self, **facets) -> list[Path]:
             for f in filename_globs
         )
 
-    def find_data(self, **facets) -> list[LocalFile]:
+    def find_data(self, **facets: FacetValue) -> list[LocalFile]:
         """Find data locally.
 
         Parameters
@@ -722,7 +724,7 @@ class DataSource(LocalDataSource):
          Please use :class:`esmvalcore.local.LocalDataSource` instead.
     """
 
-    def __init__(self, *args, **kwargs) -> None:
+    def __init__(self, *args, **kwargs):
         msg = (
             "The 'esmvalcore.local.LocalDataSource' class is deprecated and will be "
             "removed in version 2.16.0. Please use 'esmvalcore.local.LocalDataSource'"
@@ -735,7 +737,7 @@ def regex_pattern(self) -> str:
         """Get regex pattern that can be used to extract facets from paths."""
         return self._regex_pattern
 
-    def get_glob_patterns(self, **facets) -> list[Path]:
+    def get_glob_patterns(self, **facets: FacetValue) -> list[Path]:
         """Compose the globs that will be used to look for files."""
         return self._get_glob_patterns(**facets)
 
@@ -743,7 +745,7 @@ def path2facets(self, path: Path, add_timerange: bool) -> dict[str, str]:
         """Extract facets from path."""
         return self._path2facets(path, add_timerange)
 
-    def find_files(self, **facets) -> list[LocalFile]:
+    def find_files(self, **facets: FacetValue) -> list[LocalFile]:
         """Find files."""
         return self.find_data(**facets)
 
@@ -1028,7 +1030,7 @@ def _get_attr_from_field_coord(
     ncfield: iris.fileformats.cf.CFVariable,
     coord_name: str | None,
     attr: str,
-) -> Any:
+) -> Any:  # noqa: ANN401
     """Get attribute from netCDF field coordinate."""
     if coord_name is not None:
         attrs = ncfield.cf_group[coord_name].cf_attrs()
diff --git a/esmvalcore/preprocessor/__init__.py b/esmvalcore/preprocessor/__init__.py
index 8b48058d64..4cd30efa42 100644
--- a/esmvalcore/preprocessor/__init__.py
+++ b/esmvalcore/preprocessor/__init__.py
@@ -8,7 +8,7 @@
 from pprint import pformat
 from typing import TYPE_CHECKING, Any
 
-from iris.cube import Cube, CubeList
+from iris.cube import Cube
 
 from esmvalcore._provenance import TrackedFile
 from esmvalcore._task import BaseTask
@@ -107,6 +107,7 @@
 
     import prov.model
     from dask.delayed import Delayed
+    from iris.cube import CubeList
 
     from esmvalcore.dataset import Dataset
 
@@ -374,7 +375,7 @@ def _get_multi_model_settings(
 def _run_preproc_function(
     function: Callable,
     items: PreprocessorItem | Sequence[PreprocessorItem],
-    kwargs: Any,
+    kwargs: dict[str, Any],
     input_files: Sequence[DataElement] | None = None,
 ) -> PreprocessorItem | Sequence[PreprocessorItem]:
     """Run preprocessor function."""
@@ -728,7 +729,7 @@ def __init__(
         self.debug = debug
         self.write_ncl_interface = write_ncl_interface
 
-    def _run(self, _) -> list[str]:  # noqa: C901,PLR0912
+    def _run(self, _: list[str]) -> list[str]:  # noqa: C901,PLR0912
         """Run the preprocessor."""
         for product in self.products:
             product.activity = self.activity
diff --git a/esmvalcore/preprocessor/_area.py b/esmvalcore/preprocessor/_area.py
index 07ca9d25cc..0c7e08ff2a 100644
--- a/esmvalcore/preprocessor/_area.py
+++ b/esmvalcore/preprocessor/_area.py
@@ -8,16 +8,17 @@
 
 import logging
 from pathlib import Path
-from typing import TYPE_CHECKING, Literal
+from typing import TYPE_CHECKING, Any, Literal
 
 import fiona
+import fiona.collection
 import iris
 import numpy as np
 import shapely
 import shapely.ops
 from dask import array as da
 from iris.coords import AuxCoord
-from iris.cube import Cube, CubeList
+from iris.cube import CubeList
 from iris.exceptions import CoordinateNotFoundError
 
 from esmvalcore.iris_helpers import ignore_iris_vague_metadata_warnings
@@ -40,6 +41,8 @@
 if TYPE_CHECKING:
     from collections.abc import Iterable
 
+    from iris.cube import Cube
+
     from esmvalcore.config import Session
 
 logger = logging.getLogger(__name__)
@@ -211,7 +214,7 @@ def zonal_statistics(
     cube: Cube,
     operator: str,
     normalize: Literal["subtract", "divide"] | None = None,
-    **operator_kwargs,
+    **operator_kwargs: Any,
 ) -> Cube:
     """Compute zonal statistics.
 
@@ -263,7 +266,7 @@ def meridional_statistics(
     cube: Cube,
     operator: str,
     normalize: Literal["subtract", "divide"] | None = None,
-    **operator_kwargs,
+    **operator_kwargs: Any,
 ) -> Cube:
     """Compute meridional statistics.
 
@@ -318,7 +321,7 @@ def area_statistics(
     cube: Cube,
     operator: str,
     normalize: Literal["subtract", "divide"] | None = None,
-    **operator_kwargs,
+    **operator_kwargs: Any,
 ) -> Cube:
     """Apply a statistical operator in the horizontal plane.
 
@@ -477,7 +480,7 @@ def _crop_cube(
 
 
 def _select_representative_point(
-    shape,
+    shape: shapely.geometry.base.BaseGeometry,
     lon: np.ndarray,
     lat: np.ndarray,
 ) -> np.ndarray:
@@ -519,7 +522,10 @@ def _correct_coords_from_shapefile(
     return lon, lat
 
 
-def _process_ids(geometries, ids: list | dict | None) -> tuple:
+def _process_ids(
+    geometries: fiona.collection.Collection,
+    ids: list | dict | None,
+) -> tuple:
     """Read requested IDs and ID keys."""
     # If ids is a dict, it needs to have length 1 and all geometries needs to
     # have the requested attribute key
@@ -529,9 +535,7 @@ def _process_ids(geometries, ids: list | dict | None) -> tuple:
                 f"If `ids` is given as dict, it needs exactly one entry, got "
                 f"{ids}"
             )
-            raise ValueError(
-                msg,
-            )
+            raise ValueError(msg)
         key = next(iter(ids.keys()))
         for geometry in geometries:
             if key not in geometry["properties"]:
@@ -539,9 +543,7 @@ def _process_ids(geometries, ids: list | dict | None) -> tuple:
                     f"Geometry {dict(geometry['properties'])} does not have "
                     f"requested attribute {key}"
                 )
-                raise ValueError(
-                    msg,
-                )
+                raise ValueError(msg)
         id_keys: tuple[str, ...] = (key,)
         ids = ids[key]
 
@@ -559,7 +561,7 @@ def _process_ids(geometries, ids: list | dict | None) -> tuple:
 
 
 def _get_requested_geometries(
-    geometries,
+    geometries: fiona.collection.Collection,
     ids: list | dict | None,
     shapefile: Path,
 ) -> dict[str, dict]:
@@ -594,9 +596,7 @@ def _get_requested_geometries(
                 f"Requested shapes {missing} not found in shapefile "
                 f"{shapefile}"
             )
-            raise ValueError(
-                msg,
-            )
+            raise ValueError(msg)
 
     return requested_geometries
 
diff --git a/esmvalcore/preprocessor/_compare_with_refs.py b/esmvalcore/preprocessor/_compare_with_refs.py
index b58c53aab4..f0da4b4521 100644
--- a/esmvalcore/preprocessor/_compare_with_refs.py
+++ b/esmvalcore/preprocessor/_compare_with_refs.py
@@ -4,7 +4,7 @@
 
 import logging
 from functools import partial
-from typing import TYPE_CHECKING, Literal
+from typing import TYPE_CHECKING, Any, Literal
 
 import dask
 import dask.array as da
@@ -12,7 +12,7 @@
 import iris.analysis.stats
 import numpy as np
 from iris.common.metadata import CubeMetadata
-from iris.coords import CellMethod, Coord
+from iris.coords import CellMethod
 from iris.cube import Cube, CubeList
 from scipy.stats import wasserstein_distance
 
@@ -33,6 +33,8 @@
 if TYPE_CHECKING:
     from collections.abc import Iterable
 
+    from iris.coords import Coord
+
     from esmvalcore.preprocessor import PreprocessorFile
 
 logger = logging.getLogger(__name__)
@@ -165,7 +167,10 @@ def bias(
     return output_products
 
 
-def _get_ref(products, ref_tag: str) -> tuple[Cube, PreprocessorFile]:
+def _get_ref(
+    products: Iterable[PreprocessorFile],
+    ref_tag: str,
+) -> tuple[Cube, PreprocessorFile]:
     """Get reference cube and product."""
     ref_products = []
     for product in products:
@@ -230,7 +235,7 @@ def distance_metric(
     reference: Cube | None = None,
     coords: Iterable[Coord] | Iterable[str] | None = None,
     keep_reference_dataset: bool = True,
-    **kwargs,
+    **kwargs: Any,
 ) -> set[PreprocessorFile] | CubeList:
     r"""Calculate distance metrics.
 
@@ -385,7 +390,7 @@ def _calculate_metric(
     reference: Cube,
     metric: MetricType,
     coords: Iterable[Coord] | Iterable[str] | None,
-    **kwargs,
+    **kwargs: Any,
 ) -> Cube:
     """Calculate metric for a single cube relative to a reference cube."""
     # Make sure that dimensional metadata of data and ref data is compatible
@@ -475,7 +480,7 @@ def _calculate_pearsonr(
     coords: Iterable[Coord] | Iterable[str],
     *,
     weighted: bool,
-    **kwargs,
+    **kwargs: Any,
 ) -> tuple[np.ndarray | da.Array, CubeMetadata]:
     """Calculate Pearson correlation coefficient."""
     # Here, we want to use common_mask=True in iris.analysis.stats.pearsonr
diff --git a/esmvalcore/preprocessor/_concatenate.py b/esmvalcore/preprocessor/_concatenate.py
index f3425c05ec..f3142ca18a 100644
--- a/esmvalcore/preprocessor/_concatenate.py
+++ b/esmvalcore/preprocessor/_concatenate.py
@@ -59,13 +59,13 @@ def __init__(self, time: DimCoord) -> None:
         self.times = time.core_points()
         self.units = str(time.units)
 
-    def __getattr__(self, name: str) -> Any:
+    def __getattr__(self, name: str) -> Any:  # noqa: ANN401
         return getattr(self.times, name)
 
     def __len__(self) -> int:
         return len(self.times)
 
-    def __getitem__(self, key: Any) -> Any:
+    def __getitem__(self, key: Any) -> Any:  # noqa: ANN401
         return self.times[key]
 
 
@@ -219,7 +219,7 @@ def _concatenate_cubes_by_experiment(cubes: Sequence[Cube]) -> Sequence[Cube]:
         project["exp"] for project in FACETS.values() if "exp" in project
     }
 
-    def get_exp(cube: Cube) -> Any:
+    def get_exp(cube: Cube) -> str:
         for key in exp_facet_names:
             if key in cube.attributes:
                 return cube.attributes[key]
diff --git a/esmvalcore/preprocessor/_dask_progress.py b/esmvalcore/preprocessor/_dask_progress.py
index 6010f76b41..58edde625d 100644
--- a/esmvalcore/preprocessor/_dask_progress.py
+++ b/esmvalcore/preprocessor/_dask_progress.py
@@ -6,10 +6,11 @@
 import logging
 import threading
 import time
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Any
 
 import dask.diagnostics
 import distributed
+import distributed.diagnostics.progressbar
 import rich.progress
 
 from esmvalcore.config import CFG
@@ -89,7 +90,7 @@ class RichDistributedProgressBar(
     # Disable warnings about design choices that have been made in the base class.
     # pylint: disable=too-few-public-methods,unused-argument,useless-suppression
 
-    def __init__(self, keys) -> None:
+    def __init__(self, keys) -> None:  # noqa: ANN001
         self.progress = rich.progress.Progress(
             rich.progress.TaskProgressColumn(),
             rich.progress.BarColumn(bar_width=80),
@@ -106,7 +107,7 @@ def _draw_bar(
         self,
         remaining: int,
         all: int,  # noqa: A002 # pylint: disable=redefined-builtin
-        **kwargs,  # noqa: ARG002
+        **kwargs: Any,  # noqa: ARG002
     ) -> None:
         completed = all - remaining
         self.progress.update(self.task_id, completed=completed, total=all)
@@ -163,7 +164,7 @@ class DistributedProgressLogger(
 
     def __init__(
         self,
-        keys,
+        keys,  # noqa: ANN001
         log_interval: str | float = "1s",
         description: str = "",
     ) -> None:
@@ -179,7 +180,7 @@ def _draw_bar(
         self,
         remaining: int,
         all: int,  # noqa: A002 # pylint: disable=redefined-builtin
-        **kwargs,  # noqa: ARG002
+        **kwargs: Any,  # noqa: ARG002
     ) -> None:
         frac = (1 - remaining / all) if all else 1.0
         if (
diff --git a/esmvalcore/preprocessor/_derive/__init__.py b/esmvalcore/preprocessor/_derive/__init__.py
index cbf138e2d7..3a25d1f9a4 100644
--- a/esmvalcore/preprocessor/_derive/__init__.py
+++ b/esmvalcore/preprocessor/_derive/__init__.py
@@ -1,16 +1,23 @@
 """Automatically derive variables."""
 
+from __future__ import annotations
+
 import importlib
 import logging
 from copy import deepcopy
 from pathlib import Path
+from typing import TYPE_CHECKING
 
-from cf_units import Unit
-from iris.cube import Cube, CubeList
+from iris.cube import CubeList
 
-from esmvalcore.preprocessor._derive._baseclass import DerivedVariableBase
 from esmvalcore.preprocessor._units import convert_units
-from esmvalcore.typing import Facets
+
+if TYPE_CHECKING:
+    from cf_units import Unit
+    from iris.cube import Cube
+
+    from esmvalcore.preprocessor._derive._baseclass import DerivedVariableBase
+    from esmvalcore.typing import Facets
 
 logger = logging.getLogger(__name__)
 
diff --git a/esmvalcore/preprocessor/_derive/_baseclass.py b/esmvalcore/preprocessor/_derive/_baseclass.py
index b8d8bc27da..61d3187acf 100644
--- a/esmvalcore/preprocessor/_derive/_baseclass.py
+++ b/esmvalcore/preprocessor/_derive/_baseclass.py
@@ -1,10 +1,14 @@
 """Contains the base class for derived variables."""
 
+from __future__ import annotations
+
 from abc import abstractmethod
+from typing import TYPE_CHECKING
 
-from iris.cube import Cube, CubeList
+if TYPE_CHECKING:
+    from iris.cube import Cube, CubeList
 
-from esmvalcore.typing import Facets
+    from esmvalcore.typing import Facets
 
 
 class DerivedVariableBase:
diff --git a/esmvalcore/preprocessor/_derive/ohc.py b/esmvalcore/preprocessor/_derive/ohc.py
index d9105ffe52..d4db598857 100644
--- a/esmvalcore/preprocessor/_derive/ohc.py
+++ b/esmvalcore/preprocessor/_derive/ohc.py
@@ -1,14 +1,20 @@
 """Derivation of variable `ohc`."""
 
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
 import iris
 from cf_units import Unit
 from iris import Constraint
-from iris.cube import Cube, CubeList
-
-from esmvalcore.typing import Facets
 
 from ._baseclass import DerivedVariableBase
 
+if TYPE_CHECKING:
+    from iris.cube import Cube, CubeList
+
+    from esmvalcore.typing import Facets
+
 RHO_CP = iris.coords.AuxCoord(4.09169e6, units=Unit("kg m-3 J kg-1 K-1"))
 
 
diff --git a/esmvalcore/preprocessor/_derive/qep.py b/esmvalcore/preprocessor/_derive/qep.py
index 407aaba1e0..e755812b24 100644
--- a/esmvalcore/preprocessor/_derive/qep.py
+++ b/esmvalcore/preprocessor/_derive/qep.py
@@ -1,12 +1,18 @@
 """Derivation of variable `qep`."""
 
-from iris import Constraint
-from iris.cube import Cube, CubeList
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
 
-from esmvalcore.typing import Facets
+from iris import Constraint
 
 from ._baseclass import DerivedVariableBase
 
+if TYPE_CHECKING:
+    from iris.cube import Cube, CubeList
+
+    from esmvalcore.typing import Facets
+
 
 class DerivedVariable(DerivedVariableBase):
     """Derivation of variable `qep`."""
diff --git a/esmvalcore/preprocessor/_derive/vegfrac.py b/esmvalcore/preprocessor/_derive/vegfrac.py
index 419ae3878c..381c8f741f 100644
--- a/esmvalcore/preprocessor/_derive/vegfrac.py
+++ b/esmvalcore/preprocessor/_derive/vegfrac.py
@@ -1,15 +1,22 @@
 """Derivation of variable `vegFrac`."""
 
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
 import dask.array as da
 import iris
 from iris import NameConstraint
-from iris.cube import Cube, CubeList
 
 from esmvalcore.preprocessor._regrid import regrid
-from esmvalcore.typing import Facets
 
 from ._baseclass import DerivedVariableBase
 
+if TYPE_CHECKING:
+    from iris.cube import Cube, CubeList
+
+    from esmvalcore.typing import Facets
+
 
 class DerivedVariable(DerivedVariableBase):
     """Derivation of variable `vegFrac`."""
diff --git a/esmvalcore/preprocessor/_io.py b/esmvalcore/preprocessor/_io.py
index 229854cd75..57a79bf0d6 100644
--- a/esmvalcore/preprocessor/_io.py
+++ b/esmvalcore/preprocessor/_io.py
@@ -205,7 +205,7 @@ def save(  # noqa: C901
     compress: bool = False,
     alias: str = "",
     compute: bool = True,
-    **kwargs,
+    **kwargs: Any,
 ) -> Delayed | None:
     """Save iris cubes to file.
 
diff --git a/esmvalcore/preprocessor/_mask.py b/esmvalcore/preprocessor/_mask.py
index 1f363096ee..790a58b3bd 100644
--- a/esmvalcore/preprocessor/_mask.py
+++ b/esmvalcore/preprocessor/_mask.py
@@ -14,22 +14,25 @@
 import cartopy.io.shapereader as shpreader
 import dask.array as da
 import iris
+import iris.cube
 import iris.util
 import numpy as np
 import shapely.vectorized as shp_vect
 from iris.analysis import Aggregator
-from iris.util import rolling_window
 
 from esmvalcore.iris_helpers import ignore_iris_vague_metadata_warnings
-from esmvalcore.preprocessor._shared import (
-    apply_mask,
+from esmvalcore.preprocessor._shared import apply_mask
+from esmvalcore.preprocessor._supplementary_vars import (
+    register_supplementaries,
 )
 
-from ._supplementary_vars import register_supplementaries
-
 if TYPE_CHECKING:
+    from collections.abc import Sequence
+
     from iris.cube import Cube
 
+    from esmvalcore.preprocessor import PreprocessorFile
+
 logger = logging.getLogger(__name__)
 
 
@@ -217,7 +220,10 @@ def mask_landseaice(cube: Cube, mask_out: Literal["landsea", "ice"]) -> Cube:
     return cube
 
 
-def mask_glaciated(cube, mask_out: str = "glaciated"):
+def mask_glaciated(
+    cube: iris.cube.Cube,
+    mask_out: str = "glaciated",
+) -> iris.cube.Cube:
     """Mask out glaciated areas.
 
     It applies a Natural Earth mask. Note that for computational reasons
@@ -352,7 +358,7 @@ def count_spells(
     data: np.ndarray | da.Array,
     threshold: float | None,
     axis: int,
-    spell_length,
+    spell_length: int,
 ) -> np.ndarray | da.Array:
     # Copied from:
     # https://scitools-iris.readthedocs.io/en/stable/generated/gallery/general/plot_custom_aggregation.html
@@ -376,11 +382,11 @@ def count_spells(
     threshold:
         threshold point for 'significant' datapoints.
 
-    axis: int
+    axis:
         number of the array dimension mapping the time sequences.
         (Can also be negative, e.g. '-1' means last dimension)
 
-    spell_length: int
+    spell_length:
         number of consecutive times at which value > threshold to "count".
 
     Returns
@@ -406,7 +412,7 @@ def count_spells(
     # where m is a float
     ###############################################################
     with ignore_iris_vague_metadata_warnings():
-        hit_windows = rolling_window(
+        hit_windows = iris.util.rolling_window(
             data_hits,
             window=spell_length,
             step=spell_length,
@@ -616,11 +622,11 @@ def mask_multimodel(products):
 
 
 def mask_fillvalues(
-    products,
+    products: Sequence[PreprocessorFile],
     threshold_fraction: float,
     min_value: float | None = None,
     time_window: int = 1,
-):
+) -> Sequence[PreprocessorFile]:
     """Compute and apply a multi-dataset fillvalues mask.
 
     Construct the mask that fills a certain time window with missing values
@@ -632,7 +638,7 @@ def mask_fillvalues(
 
     Parameters
     ----------
-    products: iris.cube.Cube
+    products:
         data products to be masked.
 
     threshold_fraction:
@@ -648,7 +654,7 @@ def mask_fillvalues(
 
     Returns
     -------
-    iris.cube.Cube
+    :
         Masked iris cubes.
 
     Raises
diff --git a/esmvalcore/preprocessor/_multimodel.py b/esmvalcore/preprocessor/_multimodel.py
index 974090022d..f15193db4b 100644
--- a/esmvalcore/preprocessor/_multimodel.py
+++ b/esmvalcore/preprocessor/_multimodel.py
@@ -14,11 +14,13 @@
 from datetime import datetime
 from functools import reduce
 from pprint import pformat
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Any
 
 import cf_units
 import iris
-import iris.coord_categorisation
+import iris.analysis
+import iris.coords
+import iris.cube
 import numpy as np
 from iris.coords import DimCoord
 from iris.cube import Cube, CubeList
@@ -494,8 +496,8 @@ def _compute_eager(
     cubes: list,
     *,
     operator: iris.analysis.Aggregator,
-    **kwargs,
-):
+    **kwargs: Any,
+) -> iris.cube.Cube:
     """Compute statistics one slice at a time."""
     _ = [cube.data for cube in cubes]  # make sure the cubes' data are realized
 
@@ -532,8 +534,8 @@ def _compute(
     cube: iris.cube.Cube,
     *,
     operator: iris.analysis.Aggregator,
-    **kwargs,
-):
+    **kwargs: Any,
+) -> iris.cube.Cube:
     """Compute statistic."""
     # This will always return a masked array
     with ignore_iris_vague_metadata_warnings():
@@ -701,7 +703,7 @@ def multi_model_statistics(
     products: set[PreprocessorFile] | Iterable[Cube],
     span: str,
     statistics: list[str | dict],
-    output_products=None,
+    output_products: dict[str, PreprocessorFile] | None = None,
     groupby: tuple | None = None,
     keep_input_datasets: bool = True,
     ignore_scalar_coords: bool = False,
@@ -781,7 +783,7 @@ def multi_model_statistics(
         additional keyword arguments, e.g., ``[{'operator': 'percentile',
         'percent': 20}]``. All supported options are are given in
         :ref:`this table <supported_stat_operator>`.
-    output_products: dict
+    output_products:
         For internal use only. A dict with statistics names as keys and
         preprocessorfiles as values. If products are passed as input, the
         statistics cubes will be assigned to these output products.
@@ -822,7 +824,8 @@ def multi_model_statistics(
         # Avoid circular input: https://stackoverflow.com/q/16964467
         statistics_products = set()
         for group, input_prods in _group_products(products, by_key=groupby):
-            sub_output_products = output_products[group]
+            # Assume that output_products is not None if products are PreprocessorFiles.
+            sub_output_products = output_products[group]  # type: ignore[index]
 
             # Compute statistics on a single group
             group_statistics = _multiproduct_statistics(
@@ -850,7 +853,7 @@ def multi_model_statistics(
 def ensemble_statistics(
     products: set[PreprocessorFile] | Iterable[Cube],
     statistics: list[str | dict],
-    output_products,
+    output_products: dict[str, PreprocessorFile] | None,
     span: str = "overlap",
     ignore_scalar_coords: bool = False,
 ) -> dict | set:
@@ -871,7 +874,7 @@ def ensemble_statistics(
         additional keyword arguments, e.g., ``[{'operator': 'percentile',
         'percent': 20}]``. All supported options are are given in
         :ref:`this table <supported_stat_operator>`.
-    output_products: dict
+    output_products:
         For internal use only. A dict with statistics names as keys and
         preprocessorfiles as values. If products are passed as input, the
         statistics cubes will be assigned to these output products.
diff --git a/esmvalcore/preprocessor/_other.py b/esmvalcore/preprocessor/_other.py
index 6568490e1a..972f93acbb 100644
--- a/esmvalcore/preprocessor/_other.py
+++ b/esmvalcore/preprocessor/_other.py
@@ -10,7 +10,7 @@
 import dask.array as da
 import iris.analysis
 import numpy as np
-from iris.coords import Coord, DimCoord
+from iris.coords import DimCoord
 from iris.cube import Cube
 from iris.exceptions import CoordinateMultiDimError
 
@@ -31,6 +31,8 @@
 if TYPE_CHECKING:
     from collections.abc import Iterable, Sequence
 
+    from iris.coords import Coord
+
     from esmvalcore.cmor.table import VariableInfo
 
 logger = logging.getLogger(__name__)
@@ -563,7 +565,7 @@ def _get_histogram_cube(
     coords: Iterable[Coord] | Iterable[str],
     bin_edges: np.ndarray,
     normalization: Literal["sum", "integral"] | None,
-):
+) -> Cube:
     """Get cube with correct metadata for histogram."""
     # Calculate bin centers using 2-window running mean and get corresponding
     # coordinate
diff --git a/esmvalcore/preprocessor/_regrid.py b/esmvalcore/preprocessor/_regrid.py
index 11e19b9736..486b831e79 100644
--- a/esmvalcore/preprocessor/_regrid.py
+++ b/esmvalcore/preprocessor/_regrid.py
@@ -20,7 +20,11 @@
 import numpy as np
 import stratify
 from geopy.geocoders import Nominatim
-from iris.analysis import AreaWeighted, Linear, Nearest
+from iris.analysis import (
+    AreaWeighted,
+    Linear,
+    Nearest,
+)
 from iris.cube import Cube
 from iris.util import broadcast_to_shape
 
@@ -50,6 +54,7 @@
 if TYPE_CHECKING:
     from collections.abc import Iterable
 
+    from iris.analysis import Regridder, RegriddingScheme
     from numpy.typing import ArrayLike
 
     from esmvalcore.dataset import Dataset
@@ -580,7 +585,9 @@ def extract_point(
     return cube.interpolate(point, scheme=loaded_scheme)
 
 
-def is_dataset(dataset: Any) -> bool:
+def is_dataset(
+    dataset: Any,  # noqa: ANN401
+) -> bool:
     """Test if something is an `esmvalcore.dataset.Dataset`."""
     # Use this function to avoid circular imports
     return hasattr(dataset, "facets")
@@ -631,7 +638,7 @@ def _load_scheme(
     src_cube: Cube,
     tgt_cube: Cube,
     scheme: NamedHorizontalScheme | dict[str, Any],
-):
+) -> RegriddingScheme:
     """Return scheme that can be used in :meth:`iris.cube.Cube.regrid`."""
     loaded_scheme: Any = None
 
@@ -664,7 +671,7 @@ def _load_scheme(
     return loaded_scheme
 
 
-def _load_generic_scheme(scheme: dict[str, Any]):
+def _load_generic_scheme(scheme: dict[str, Any]) -> RegriddingScheme:
     """Load generic regridding scheme."""
     scheme = dict(scheme)  # do not overwrite original scheme
 
@@ -706,7 +713,7 @@ def _get_regridder(
     tgt_cube: Cube,
     scheme: NamedHorizontalScheme | dict,
     cache_weights: bool,
-):
+) -> Regridder:
     """Get regridder to actually perform regridding.
 
     Note
diff --git a/esmvalcore/preprocessor/_rolling_window.py b/esmvalcore/preprocessor/_rolling_window.py
index 87c9c56711..fc868de2ea 100644
--- a/esmvalcore/preprocessor/_rolling_window.py
+++ b/esmvalcore/preprocessor/_rolling_window.py
@@ -1,8 +1,9 @@
 """Rolling-window operations on data cubes."""
 
-import logging
+from __future__ import annotations
 
-from iris.cube import Cube
+import logging
+from typing import TYPE_CHECKING, Any
 
 from esmvalcore.iris_helpers import ignore_iris_vague_metadata_warnings
 
@@ -11,6 +12,9 @@
     preserve_float_dtype,
 )
 
+if TYPE_CHECKING:
+    from iris.cube import Cube
+
 logger = logging.getLogger(__name__)
 
 
@@ -20,8 +24,8 @@ def rolling_window_statistics(
     coordinate: str,
     operator: str,
     window_length: int,
-    **operator_kwargs,
-):
+    **operator_kwargs: Any,
+) -> Cube:
     """Compute rolling-window statistics over a coordinate.
 
     Parameters
diff --git a/esmvalcore/preprocessor/_shared.py b/esmvalcore/preprocessor/_shared.py
index abb717d2f9..ecf58028e2 100644
--- a/esmvalcore/preprocessor/_shared.py
+++ b/esmvalcore/preprocessor/_shared.py
@@ -16,7 +16,7 @@
 import dask.array as da
 import iris.analysis
 import numpy as np
-from iris.coords import CellMeasure, Coord, DimCoord
+from iris.coords import CellMeasure, DimCoord
 from iris.cube import Cube
 from iris.exceptions import CoordinateMultiDimError, CoordinateNotFoundError
 from iris.util import broadcast_to_shape
@@ -29,6 +29,8 @@
 if TYPE_CHECKING:
     from collections.abc import Callable, Iterable
 
+    from iris.coords import Coord
+
     from esmvalcore.typing import DataType
 
 logger = logging.getLogger(__name__)
@@ -45,7 +47,7 @@ def guess_bounds(cube, coords):
 
 def get_iris_aggregator(
     operator: str,
-    **operator_kwargs,
+    **operator_kwargs: Any,
 ) -> tuple[iris.analysis.Aggregator, dict]:
     """Get :class:`iris.analysis.Aggregator` and keyword arguments.
 
@@ -82,18 +84,14 @@ def get_iris_aggregator(
     # Check if valid aggregator is found
     if not hasattr(iris.analysis, cap_operator):
         msg = f"Aggregator '{operator}' not found in iris.analysis module"
-        raise ValueError(
-            msg,
-        )
+        raise ValueError(msg)
     aggregator = getattr(iris.analysis, cap_operator)
     if not hasattr(aggregator, "aggregate"):
         msg = (
             f"Aggregator {aggregator} found by '{operator}' is not a valid "
             f"iris.analysis.Aggregator"
         )
-        raise ValueError(
-            msg,
-        )
+        raise ValueError(msg)
 
     # Use dummy cube to check if aggregator_kwargs are valid
     x_coord = DimCoord([1.0], bounds=[0.0, 2.0], var_name="x")
@@ -109,9 +107,7 @@ def get_iris_aggregator(
             cube.collapsed("x", aggregator, **test_kwargs)
     except (ValueError, TypeError) as exc:
         msg = f"Invalid kwargs for operator '{operator}': {exc!s}"
-        raise ValueError(
-            msg,
-        ) from exc
+        raise ValueError(msg) from exc
 
     return (aggregator, aggregator_kwargs)
 
@@ -141,10 +137,10 @@ def update_weights_kwargs(
     operator: str,
     aggregator: iris.analysis.Aggregator,
     kwargs: dict,
-    weights: Any,
+    weights: Any,  # noqa: ANN401
     cube: Cube | None = None,
     callback: Callable | None = None,
-    **callback_kwargs,
+    **callback_kwargs: Any,
 ) -> dict:
     """Update weights keyword argument.
 
@@ -248,7 +244,7 @@ def get_normalized_cube(
     return normalized_cube
 
 
-def _get_first_arg(func: Callable, *args: Any, **kwargs: Any) -> Any:
+def _get_first_arg(func: Callable, *args: Any, **kwargs: Any) -> Any:  # noqa: ANN401
     """Get first argument given to a function."""
     # If positional arguments are given, use the first one
     if args:
diff --git a/esmvalcore/preprocessor/_supplementary_vars.py b/esmvalcore/preprocessor/_supplementary_vars.py
index 401498f047..f7a1491d09 100644
--- a/esmvalcore/preprocessor/_supplementary_vars.py
+++ b/esmvalcore/preprocessor/_supplementary_vars.py
@@ -1,11 +1,16 @@
 """Preprocessor functions for ancillary variables and cell measures."""
 
+from __future__ import annotations
+
 import logging
-from collections.abc import Callable, Iterable
-from typing import Literal
+from typing import TYPE_CHECKING, Literal
 
 import iris.coords
-from iris.cube import Cube
+
+if TYPE_CHECKING:
+    from collections.abc import Callable, Iterable
+
+    from iris.cube import Cube
 
 logger = logging.getLogger(__name__)
 
diff --git a/esmvalcore/preprocessor/_time.py b/esmvalcore/preprocessor/_time.py
index cb2f5a72e5..ee548afc69 100644
--- a/esmvalcore/preprocessor/_time.py
+++ b/esmvalcore/preprocessor/_time.py
@@ -11,7 +11,7 @@
 import logging
 import warnings
 from functools import partial
-from typing import TYPE_CHECKING, Literal
+from typing import TYPE_CHECKING, Any, Literal
 from warnings import filterwarnings
 
 import dask.array as da
@@ -24,8 +24,8 @@
 import numpy as np
 from cf_units import Unit
 from cftime import datetime as cf_datetime
-from iris.coords import AuxCoord, Coord, DimCoord
-from iris.cube import Cube, CubeList
+from iris.coords import AuxCoord, DimCoord
+from iris.cube import CubeList
 from iris.exceptions import CoordinateMultiDimError, CoordinateNotFoundError
 from iris.time import PartialDateTime
 from iris.util import broadcast_to_shape
@@ -46,6 +46,8 @@
 if TYPE_CHECKING:
     from collections.abc import Iterable
 
+    from iris.coords import Coord
+    from iris.cube import Cube
     from numpy.typing import DTypeLike
 
 logger = logging.getLogger(__name__)
@@ -494,7 +496,7 @@ def hourly_statistics(
     cube: Cube,
     hours: int,
     operator: str = "mean",
-    **operator_kwargs,
+    **operator_kwargs: Any,
 ) -> Cube:
     """Compute hourly statistics.
 
@@ -552,7 +554,7 @@ def hourly_statistics(
 def daily_statistics(
     cube: Cube,
     operator: str = "mean",
-    **operator_kwargs,
+    **operator_kwargs: Any,
 ) -> Cube:
     """Compute daily statistics.
 
@@ -593,7 +595,7 @@ def daily_statistics(
 def monthly_statistics(
     cube: Cube,
     operator: str = "mean",
-    **operator_kwargs,
+    **operator_kwargs: Any,
 ) -> Cube:
     """Compute monthly statistics.
 
@@ -637,7 +639,7 @@ def seasonal_statistics(
     cube: Cube,
     operator: str = "mean",
     seasons: Iterable[str] = ("DJF", "MAM", "JJA", "SON"),
-    **operator_kwargs,
+    **operator_kwargs: Any,
 ) -> Cube:
     """Compute seasonal statistics.
 
@@ -747,7 +749,7 @@ def spans_full_season(cube: Cube) -> list[bool]:
 def annual_statistics(
     cube: Cube,
     operator: str = "mean",
-    **operator_kwargs,
+    **operator_kwargs: Any,
 ) -> Cube:
     """Compute annual statistics.
 
@@ -789,7 +791,7 @@ def annual_statistics(
 def decadal_statistics(
     cube: Cube,
     operator: str = "mean",
-    **operator_kwargs,
+    **operator_kwargs: Any,
 ) -> Cube:
     """Compute decadal statistics.
 
@@ -844,7 +846,7 @@ def climate_statistics(
     operator: str = "mean",
     period: str = "full",
     seasons: Iterable[str] = ("DJF", "MAM", "JJA", "SON"),
-    **operator_kwargs,
+    **operator_kwargs: Any,
 ) -> Cube:
     """Compute climate statistics with the specified granularity.
 
@@ -1068,7 +1070,7 @@ def _compute_anomalies(
     reference: Cube,
     period: str,
     seasons: Iterable[str],
-):
+) -> Cube:
     cube_coord = _get_period_coord(cube, period, seasons)
     ref_coord = _get_period_coord(reference, period, seasons)
     indices = np.empty_like(cube_coord.points, dtype=np.int32)
@@ -1340,7 +1342,7 @@ def timeseries_filter(
     span: int,
     filter_type: str = "lowpass",
     filter_stats: str = "sum",
-    **operator_kwargs,
+    **operator_kwargs: Any,
 ) -> Cube:
     """Apply a timeseries filter.
 
@@ -1723,7 +1725,7 @@ def _transform_to_lst_eager(
     *,
     time_dim: int,
     lon_dim: int,
-    **__,
+    **__: Any,
 ) -> np.ndarray:
     """Transform array with UTC coord to local solar time (LST) coord.
 
diff --git a/esmvalcore/preprocessor/_units.py b/esmvalcore/preprocessor/_units.py
index 5d34d42c9c..413a289066 100644
--- a/esmvalcore/preprocessor/_units.py
+++ b/esmvalcore/preprocessor/_units.py
@@ -11,12 +11,13 @@
 import dask.array as da
 import iris
 import numpy as np
-from iris.coords import AuxCoord, DimCoord
+from iris.coords import AuxCoord
 
 from esmvalcore.iris_helpers import _try_special_unit_conversions
 
 if TYPE_CHECKING:
     from cf_units import Unit
+    from iris.coords import DimCoord
     from iris.cube import Cube
 
 logger = logging.getLogger(__name__)
diff --git a/esmvalcore/preprocessor/_volume.py b/esmvalcore/preprocessor/_volume.py
index f6f5b1f494..aefd15c8c1 100644
--- a/esmvalcore/preprocessor/_volume.py
+++ b/esmvalcore/preprocessor/_volume.py
@@ -7,7 +7,7 @@
 from __future__ import annotations
 
 import logging
-from typing import TYPE_CHECKING, Literal
+from typing import TYPE_CHECKING, Any, Literal
 
 import dask
 import dask.array as da
@@ -250,7 +250,7 @@ def volume_statistics(
     cube: Cube,
     operator: str,
     normalize: Literal["subtract", "divide"] | None = None,
-    **operator_kwargs,
+    **operator_kwargs: Any,
 ) -> Cube:
     """Apply a statistical operation over a volume.
 
@@ -346,7 +346,7 @@ def axis_statistics(
     axis: str,
     operator: str,
     normalize: Literal["subtract", "divide"] | None = None,
-    **operator_kwargs,
+    **operator_kwargs: Any,
 ) -> Cube:
     """Perform statistics along a given axis.
 
diff --git a/esmvalcore/preprocessor/regrid_schemes.py b/esmvalcore/preprocessor/regrid_schemes.py
index 01247ebc42..5fbc5f0359 100644
--- a/esmvalcore/preprocessor/regrid_schemes.py
+++ b/esmvalcore/preprocessor/regrid_schemes.py
@@ -3,7 +3,7 @@
 from __future__ import annotations
 
 import logging
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Any
 
 from esmvalcore.preprocessor._regrid_iris_esmf_regrid import IrisESMFRegrid
 from esmvalcore.preprocessor._regrid_unstructured import (
@@ -53,8 +53,8 @@ def __init__(
         src_cube: Cube,
         tgt_cube: Cube,
         func: Callable,
-        **kwargs,
-    ):
+        **kwargs: Any,
+    ) -> None:
         """Initialize class instance."""
         self.src_cube = src_cube
         self.tgt_cube = tgt_cube
@@ -93,7 +93,7 @@ class GenericFuncScheme:
         Keyword arguments for the generic regridding function.
     """
 
-    def __init__(self, func: Callable, **kwargs):
+    def __init__(self, func: Callable, **kwargs: Any) -> None:
         """Initialize class instance."""
         self.func = func
         self.kwargs = kwargs
diff --git a/pyproject.toml b/pyproject.toml
index dfc0cb0b0b..158c455725 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -182,7 +182,6 @@ line-length = 79
 select = ["ALL"]
 ignore = [
     # Ignore until someone has time to fix this:
-    "ANN",      # Adding type hints
     "DTZ",      # add tzinfo to datetimes
     "FBT",      # avoid boolean positional arguments
     "N818",     # Exception name should be named with an Error suffix
@@ -207,6 +206,7 @@ ignore = [
     "TD002",    # Missing author in TODO: can be seen from git history
     "TRY003",   # Fixing this would require many exceptions
 ]
+future-annotations = true
 [tool.ruff.lint.per-file-ignores]
 "**.ipynb" = [
     "T20",      # Printing things in notebooks is fine.
@@ -225,9 +225,9 @@ ignore = [
     "D104",     # Missing docstring in public package
     "PT013",    # Allow importing fixtures from pytest to avoid repeating 'pytest' many times
 ]
-"doc/gensidebar.py" = [
-    "INP001",   # File is part of an implicit namespace package
-]
+[tool.ruff.lint.flake8-annotations]
+allow-star-arg-any = true
+ignore-fully-untyped = true
 [tool.ruff.lint.isort]
 known-first-party = ["esmvalcore"]
 [tool.ruff.lint.pydocstyle]
diff --git a/tests/conftest.py b/tests/conftest.py
index 1cc8630b88..46cabf58f9 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1,7 +1,9 @@
+from __future__ import annotations
+
 import warnings
 from copy import deepcopy
 from functools import lru_cache
-from pathlib import Path
+from typing import TYPE_CHECKING
 
 import numpy as np
 import pytest
@@ -17,6 +19,11 @@
 
 from esmvalcore.config import CFG, Config
 
+if TYPE_CHECKING:
+    from pathlib import Path
+
+    from esmvalcore.config import Session
+
 
 @lru_cache
 def _load_default_config():
@@ -40,13 +47,20 @@ def cfg_default():
 
 
 @pytest.fixture(autouse=True)
-def ignore_existing_user_config(monkeypatch, cfg_default):
+def ignore_existing_user_config(
+    monkeypatch: pytest.MonkeyPatch,
+    cfg_default: Config,
+) -> None:
     """Ignore user's configuration when running tests."""
     monkeypatch.setattr(CFG, "_mapping", cfg_default._mapping)
 
 
 @pytest.fixture
-def session(tmp_path: Path, ignore_existing_user_config, monkeypatch):
+def session(
+    tmp_path: Path,
+    ignore_existing_user_config: None,
+    monkeypatch: pytest.MonkeyPatch,
+) -> Session:
     """Session object with default settings."""
     monkeypatch.setitem(CFG, "output_dir", tmp_path / "esmvaltool_output")
     return CFG.start_session("recipe_test")
diff --git a/tests/integration/cmor/_fixes/icon/conftest.py b/tests/integration/cmor/_fixes/icon/conftest.py
index e8f323c175..961aff4755 100644
--- a/tests/integration/cmor/_fixes/icon/conftest.py
+++ b/tests/integration/cmor/_fixes/icon/conftest.py
@@ -1,7 +1,9 @@
 """Fixtures for ICON fixes tests."""
 
+from __future__ import annotations
+
 import importlib.resources
-from pathlib import Path
+from typing import TYPE_CHECKING
 
 import pytest
 import yaml
@@ -9,6 +11,9 @@
 import esmvalcore.config
 from esmvalcore.cmor._fixes.icon._base_fixes import IconFix
 
+if TYPE_CHECKING:
+    from pathlib import Path
+
 
 @pytest.fixture(autouse=True)
 def tmp_cache_dir(monkeypatch, tmp_path):
diff --git a/tests/integration/conftest.py b/tests/integration/conftest.py
index 85b1505866..bb5f4a0324 100644
--- a/tests/integration/conftest.py
+++ b/tests/integration/conftest.py
@@ -1,6 +1,8 @@
+from __future__ import annotations
+
 import os
-from collections.abc import Iterator
 from pathlib import Path
+from typing import TYPE_CHECKING
 
 import iris
 import pytest
@@ -12,7 +14,11 @@
     _select_drs,
     _select_files,
 )
-from esmvalcore.typing import Facets
+
+if TYPE_CHECKING:
+    from collections.abc import Callable, Iterator
+
+    from esmvalcore.typing import Facets, FacetValue
 
 
 def create_test_file(filename, tracking_id=None):
@@ -123,10 +129,21 @@ def _tracking_ids(i=0):
         i += 1
 
 
-def _get_find_files_func(path: Path, suffix: str = "nc"):
+def _get_find_files_func(
+    path: Path,
+    suffix: str = "nc",
+) -> Callable[
+    ...,
+    tuple[list[LocalFile], list[Path]] | list[LocalFile],
+]:
     tracking_id = _tracking_ids()
 
-    def find_files(self, *, debug: bool = False, **facets):
+    def find_files(
+        self: esmvalcore.local.LocalDataSource,
+        *,
+        debug: bool = False,
+        **facets: FacetValue,
+    ) -> tuple[list[LocalFile], list[Path]] | list[LocalFile]:
         files, file_globs = _get_files(path, facets, tracking_id, suffix)
         if debug:
             return files, file_globs
@@ -136,7 +153,7 @@ def find_files(self, *, debug: bool = False, **facets):
 
 
 @pytest.fixture
-def patched_datafinder(tmp_path, monkeypatch):
+def patched_datafinder(tmp_path: Path, monkeypatch: pytest.MonkeyPath) -> None:
     find_files = _get_find_files_func(tmp_path)
     monkeypatch.setattr(
         esmvalcore.local.LocalDataSource,
@@ -146,7 +163,10 @@ def patched_datafinder(tmp_path, monkeypatch):
 
 
 @pytest.fixture
-def patched_datafinder_grib(tmp_path, monkeypatch):
+def patched_datafinder_grib(
+    tmp_path: Path,
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
     find_files = _get_find_files_func(tmp_path, suffix="grib")
     monkeypatch.setattr(
         esmvalcore.local.LocalDataSource,
@@ -156,7 +176,10 @@ def patched_datafinder_grib(tmp_path, monkeypatch):
 
 
 @pytest.fixture
-def patched_failing_datafinder(tmp_path, monkeypatch):
+def patched_failing_datafinder(
+    tmp_path: Path,
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
     """Failing data finder.
 
     Do not return files for:
@@ -168,7 +191,12 @@ def patched_failing_datafinder(tmp_path, monkeypatch):
     """
     tracking_id = _tracking_ids()
 
-    def find_files(self, *, debug: bool = False, **facets):
+    def find_files(
+        self: esmvalcore.local.LocalDataSource,
+        *,
+        debug: bool = False,
+        **facets: FacetValue,
+    ) -> tuple[list[LocalFile], list[Path]] | list[LocalFile]:
         files, file_globs = _get_files(tmp_path, facets, tracking_id)
         if facets["frequency"] == "fx":
             files = []
diff --git a/tests/integration/recipe/test_check.py b/tests/integration/recipe/test_check.py
index 3879b46724..19fd6b01ca 100644
--- a/tests/integration/recipe/test_check.py
+++ b/tests/integration/recipe/test_check.py
@@ -1,12 +1,14 @@
 """Integration tests for :mod:`esmvalcore._recipe.check`."""
 
+from __future__ import annotations
+
 import subprocess
 from pathlib import Path
+from typing import TYPE_CHECKING
 from unittest import mock
 
 import pyesgf.search.results
 import pytest
-import pytest_mock
 
 import esmvalcore._recipe.check
 import esmvalcore.esgf
@@ -16,6 +18,9 @@
 from esmvalcore.local import LocalFile
 from esmvalcore.preprocessor import PreprocessorFile
 
+if TYPE_CHECKING:
+    import pytest_mock
+
 
 def test_ncl_version(mocker):
     ncl = "/path/to/ncl"
diff --git a/tests/integration/recipe/test_recipe.py b/tests/integration/recipe/test_recipe.py
index 6b8b788173..10801a671e 100644
--- a/tests/integration/recipe/test_recipe.py
+++ b/tests/integration/recipe/test_recipe.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import importlib.resources
 import inspect
 import os
@@ -24,7 +26,6 @@
     read_recipe_file,
 )
 from esmvalcore._task import DiagnosticTask
-from esmvalcore.config import Session
 from esmvalcore.config._config import TASKSEP
 from esmvalcore.config._diagnostics import TAGS
 from esmvalcore.dataset import Dataset
@@ -34,12 +35,16 @@
 from tests.integration.test_provenance import check_provenance
 
 if TYPE_CHECKING:
+    from esmvalcore._recipe.recipe import (
+        Recipe,
+    )
+    from esmvalcore.config import Session
     from esmvalcore.typing import Facets
 
 
 @lru_cache
 def _load_data_sources(
-    filename,
+    filename: str,
 ) -> dict[
     str,
     dict[str, dict[str, dict[str, dict[str, str]]]],
@@ -193,7 +198,7 @@ def get_required(short_name, _):
     """)
 
 
-def get_recipe(tempdir: Path, content: str, session: Session):
+def get_recipe(tempdir: Path, content: str, session: Session) -> Recipe:
     """Save and load recipe content."""
     recipe_file = tempdir / "recipe_test.yml"
     # Add mandatory documentation section
@@ -2538,7 +2543,7 @@ def test_representative_dataset_regular_var(
     tmp_path: Path,
     patched_datafinder: None,
     session: Session,
-):
+) -> None:
     """Test ``_representative_dataset`` with regular variable."""
     update_data_sources(session, "data-native-icon.yml", tmp_path)
 
@@ -2567,7 +2572,7 @@ def test_representative_dataset_derived_var(
     patched_datafinder: None,
     session: Session,
     force_derivation: bool,
-):
+) -> None:
     """Test ``_representative_dataset`` with derived variable."""
     update_data_sources(session, "data-native-icon.yml", tmp_path)
 
diff --git a/tests/integration/test_main.py b/tests/integration/test_main.py
index c701e35af9..90a86da39a 100644
--- a/tests/integration/test_main.py
+++ b/tests/integration/test_main.py
@@ -3,13 +3,15 @@
 Includes a context manager to temporarily modify sys.argv
 """
 
+from __future__ import annotations
+
 import contextlib
 import copy
 import functools
 import sys
 import warnings
-from pathlib import Path
 from textwrap import dedent
+from typing import TYPE_CHECKING
 from unittest.mock import patch
 
 import pytest
@@ -21,6 +23,9 @@
 from esmvalcore._main import Config, ESMValTool, Recipes, run
 from esmvalcore.exceptions import RecipeError
 
+if TYPE_CHECKING:
+    from pathlib import Path
+
 
 def wrapper(f):
     @functools.wraps(f)
diff --git a/tests/sample_data/multimodel_statistics/test_multimodel.py b/tests/sample_data/multimodel_statistics/test_multimodel.py
index 84376465d8..a52ba001af 100644
--- a/tests/sample_data/multimodel_statistics/test_multimodel.py
+++ b/tests/sample_data/multimodel_statistics/test_multimodel.py
@@ -1,9 +1,12 @@
 """Test using sample data for :func:`esmvalcore.preprocessor._multimodel`."""
 
+from __future__ import annotations
+
 import pickle
 import platform
 from itertools import groupby
 from pathlib import Path
+from typing import TYPE_CHECKING
 
 import cf_units
 import iris
@@ -14,6 +17,9 @@
 from esmvalcore.preprocessor import extract_time
 from esmvalcore.preprocessor._multimodel import multi_model_statistics
 
+if TYPE_CHECKING:
+    from collections.abc import Sequence
+
 esmvaltool_sample_data = pytest.importorskip("esmvaltool_sample_data")
 
 # Increase this number anytime you change the cached input data to the tests.
@@ -30,7 +36,7 @@ def assert_array_almost_equal(this, other, rtol=1e-7):
     np.testing.assert_allclose(this, other, rtol=rtol)
 
 
-def assert_coords_equal(this: list, other: list):
+def assert_coords_equal(this: list, other: list) -> None:
     """Assert coords list `this` equals coords list `other`."""
     for this_coord, other_coord in zip(this, other, strict=False):
         np.testing.assert_equal(this_coord.points, other_coord.points)
@@ -53,7 +59,10 @@ def fix_metadata(cubes):
         cube.coord("air_pressure").bounds = None
 
 
-def preprocess_data(cubes, time_slice: dict | None = None):
+def preprocess_data(
+    cubes: Sequence[iris.cube.Cube],
+    time_slice: dict | None = None,
+) -> list[iris.cube.Cube]:
     """Regrid the data to the first cube and optional time-slicing."""
     # Increase TEST_REVISION anytime you make changes to this function.
     if time_slice:
diff --git a/tests/unit/config/test_config.py b/tests/unit/config/test_config.py
index 266795c616..3bd3fcc566 100644
--- a/tests/unit/config/test_config.py
+++ b/tests/unit/config/test_config.py
@@ -28,7 +28,7 @@
         for f in BUILTIN_CONFIG_DIR.rglob("*.yml")
     ],
 )
-def test_builtin_config_files_have_description(config_file) -> None:
+def test_builtin_config_files_have_description(config_file: Path) -> None:
     """Test that all built-in config files have a description."""
     # Use the same code to find the description as in the
     # `esmvaltool config list` command.
diff --git a/tests/unit/config/test_data_sources.py b/tests/unit/config/test_data_sources.py
index 67b364018c..b1e08f69af 100644
--- a/tests/unit/config/test_data_sources.py
+++ b/tests/unit/config/test_data_sources.py
@@ -1,10 +1,16 @@
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
 import pytest
 
 import esmvalcore.config._data_sources
 import esmvalcore.local
-from esmvalcore.config import Session
 from esmvalcore.exceptions import InvalidConfigParameter
 
+if TYPE_CHECKING:
+    from esmvalcore.config import Session
+
 
 def test_load_data_sources_no_project_data_sources_configured(
     session: Session,
diff --git a/tests/unit/esgf/test_download.py b/tests/unit/esgf/test_download.py
index 9c36477b76..886e76404e 100644
--- a/tests/unit/esgf/test_download.py
+++ b/tests/unit/esgf/test_download.py
@@ -1,21 +1,26 @@
 """Test `esmvalcore.esgf._download`."""
 
+from __future__ import annotations
+
 import datetime
 import logging
 import os
 import re
 import textwrap
 from pathlib import Path
+from typing import TYPE_CHECKING
 
 import pytest
 import requests
 import yaml
 from pyesgf.search.results import FileResult
-from pytest_mock import MockerFixture
 
 import esmvalcore.esgf
 from esmvalcore.esgf import _download
 
+if TYPE_CHECKING:
+    from pytest_mock import MockerFixture
+
 
 def test_log_speed(monkeypatch, tmp_path):
     hosts_file = tmp_path / ".esmvaltool" / "cache" / "esgf-hosts.yml"
diff --git a/tests/unit/esgf/test_search.py b/tests/unit/esgf/test_search.py
index 5949cc5792..a1b8147e89 100644
--- a/tests/unit/esgf/test_search.py
+++ b/tests/unit/esgf/test_search.py
@@ -1,18 +1,23 @@
 """Test 1esmvalcore.esgf._search`."""
 
+from __future__ import annotations
+
 import copy
 import textwrap
 from pathlib import Path
+from typing import TYPE_CHECKING
 
 import pyesgf.search
 import pytest
 import requests.exceptions
 from pyesgf.search.results import FileResult
-from pytest_mock import MockerFixture
 
 import esmvalcore.io.protocol
 from esmvalcore.esgf import ESGFDataSource, ESGFFile, _search, find_files
 
+if TYPE_CHECKING:
+    from pytest_mock import MockerFixture
+
 OUR_FACETS = (
     {
         "dataset": "cccma_cgcm3_1",
diff --git a/tests/unit/io/test_intake_esgf.py b/tests/unit/io/test_intake_esgf.py
index a72e145eae..b24fc698b0 100644
--- a/tests/unit/io/test_intake_esgf.py
+++ b/tests/unit/io/test_intake_esgf.py
@@ -1,6 +1,9 @@
 """Unit tests for esmvalcore.io.intake_esgf."""
 
+from __future__ import annotations
+
 import importlib.resources
+from typing import TYPE_CHECKING
 
 import intake_esgf
 import iris.cube
@@ -8,13 +11,16 @@
 import pytest
 import xarray as xr
 import yaml
-from pytest import MonkeyPatch
-from pytest_mock import MockerFixture
 
 import esmvalcore.io.intake_esgf
-from esmvalcore.config import Session
 from esmvalcore.io.intake_esgf import IntakeESGFDataset, IntakeESGFDataSource
 
+if TYPE_CHECKING:
+    from pytest import MonkeyPatch
+    from pytest_mock import MockerFixture
+
+    from esmvalcore.config import Session
+
 
 def test_intakeesgfdataset_repr() -> None:
     cat = intake_esgf.ESGFCatalog()
@@ -134,7 +140,7 @@ def test_find_data_no_results_sets_debug_info(mocker: MockerFixture) -> None:
     assert data_source.debug_info == expected_debug_info
 
 
-def test_find_data(mocker: MockerFixture, monkeypatch: MonkeyPatch):
+def test_find_data(mocker: MockerFixture, monkeypatch: MonkeyPatch) -> None:
     """find_data should convert catalog.df rows into IntakeESGFDataset instances."""
     cat = intake_esgf.ESGFCatalog()
     cat.project = intake_esgf.projects.projects["cmip6"]
diff --git a/tests/unit/io/test_load_data_sources.py b/tests/unit/io/test_load_data_sources.py
index de1f7bad23..d6f7dd380b 100644
--- a/tests/unit/io/test_load_data_sources.py
+++ b/tests/unit/io/test_load_data_sources.py
@@ -6,7 +6,7 @@
 import pytest
 
 import esmvalcore.config
-import esmvalcore.io
+import esmvalcore.io.protocol
 
 
 def test_configurations_valid(cfg_default: esmvalcore.config.Config) -> None:
@@ -19,7 +19,7 @@ def test_configurations_valid(cfg_default: esmvalcore.config.Config) -> None:
     session = cfg_default.start_session("test")
     data_sources = esmvalcore.io.load_data_sources(session)
     for data_source in data_sources:
-        assert isinstance(data_source, esmvalcore.io.DataSource)
+        assert isinstance(data_source, esmvalcore.io.protocol.DataSource)
 
 
 def test_load_data_sources_unknown_project(
diff --git a/tests/unit/local/test_get_data_sources.py b/tests/unit/local/test_get_data_sources.py
index 4c0e7be5d5..67057562df 100644
--- a/tests/unit/local/test_get_data_sources.py
+++ b/tests/unit/local/test_get_data_sources.py
@@ -1,12 +1,17 @@
+from __future__ import annotations
+
 from pathlib import Path
+from typing import TYPE_CHECKING
 
 import pytest
-import pytest_mock
 
 from esmvalcore.config import CFG
 from esmvalcore.config._config_validators import validate_config_developer
 from esmvalcore.local import DataSource, LocalDataSource, _get_data_sources
 
+if TYPE_CHECKING:
+    import pytest_mock
+
 
 @pytest.mark.parametrize(
     "rootpath_drs",
diff --git a/tests/unit/local/test_to_iris.py b/tests/unit/local/test_to_iris.py
index 44a6a881d3..cae3db2599 100644
--- a/tests/unit/local/test_to_iris.py
+++ b/tests/unit/local/test_to_iris.py
@@ -1,11 +1,17 @@
-from pathlib import Path
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
 
 import iris.cube
 import pytest
-from pytest_mock import MockerFixture
 
 from esmvalcore.local import LocalFile, _get_attr_from_field_coord
 
+if TYPE_CHECKING:
+    from pathlib import Path
+
+    from pytest_mock import MockerFixture
+
 
 @pytest.fixture
 def local_file(tmp_path: Path) -> LocalFile:
diff --git a/tests/unit/preprocessor/_regrid/__init__.py b/tests/unit/preprocessor/_regrid/__init__.py
index 5a99c5115f..c9938e051d 100644
--- a/tests/unit/preprocessor/_regrid/__init__.py
+++ b/tests/unit/preprocessor/_regrid/__init__.py
@@ -40,7 +40,7 @@ def _make_cube(  # noqa: PLR0915,C901
     data: np.ndarray,
     aux_coord: bool = True,
     dim_coord: bool = True,
-    dtype=None,
+    dtype=None,  # noqa: ANN001
     grid: Literal["regular", "rotated", "mesh"] = "regular",
 ) -> iris.cube.Cube:
     """Create a 3d synthetic test cube."""
diff --git a/tests/unit/preprocessor/_regrid/test_regrid.py b/tests/unit/preprocessor/_regrid/test_regrid.py
index a81cc49504..7b41305c7e 100644
--- a/tests/unit/preprocessor/_regrid/test_regrid.py
+++ b/tests/unit/preprocessor/_regrid/test_regrid.py
@@ -25,7 +25,13 @@ def clear_regridder_cache(monkeypatch):
     )
 
 
-def _make_coord(start: float, stop: float, step: int, *, name: str):
+def _make_coord(
+    start: float,
+    stop: float,
+    step: int,
+    *,
+    name: str,
+) -> iris.coords.DimCoord:
     """Create a latitude or longitude coordinate with bounds."""
     coord = iris.coords.DimCoord(
         np.linspace(start, stop, step),
@@ -36,7 +42,7 @@ def _make_coord(start: float, stop: float, step: int, *, name: str):
     return coord
 
 
-def _make_cube(*, lat: tuple, lon: tuple):
+def _make_cube(*, lat: tuple, lon: tuple) -> iris.cube.Cube:
     """Create a cube with a latitude and longitude dimension."""
     lat_coord = _make_coord(*lat, name="latitude")
     lon_coord = _make_coord(*lon, name="longitude")
@@ -224,7 +230,7 @@ def test_regrid_generic_regridding(cache_weights, cube_10x10, cube_30x30):
         ),
     ],
 )
-def test_horizontal_grid_is_close(cube2_spec: dict, expected: bool):
+def test_horizontal_grid_is_close(cube2_spec: dict, expected: bool) -> None:
     """Test for `_horizontal_grid_is_close`."""
     cube1 = _make_cube(lat=LAT_SPEC1, lon=LON_SPEC1)
     cube2 = _make_cube(**cube2_spec)
diff --git a/tests/unit/provenance/test_trackedfile.py b/tests/unit/provenance/test_trackedfile.py
index 16290ec72b..8035962b49 100644
--- a/tests/unit/provenance/test_trackedfile.py
+++ b/tests/unit/provenance/test_trackedfile.py
@@ -1,9 +1,9 @@
+from __future__ import annotations
+
 from dataclasses import dataclass
 from pathlib import Path
-from typing import Any
+from typing import TYPE_CHECKING, Any
 
-import iris.cube
-import prov.model
 import pytest
 from prov.model import ProvDocument
 
@@ -11,6 +11,10 @@
 from esmvalcore.io.protocol import DataElement
 from esmvalcore.local import LocalFile
 
+if TYPE_CHECKING:
+    import iris.cube
+    import prov.model
+
 
 def test_set() -> None:
     assert {
diff --git a/tests/unit/recipe/test_to_datasets.py b/tests/unit/recipe/test_to_datasets.py
index 675c538e69..4369a815fa 100644
--- a/tests/unit/recipe/test_to_datasets.py
+++ b/tests/unit/recipe/test_to_datasets.py
@@ -1,8 +1,10 @@
+from __future__ import annotations
+
 import textwrap
 from pathlib import Path
+from typing import TYPE_CHECKING
 
 import pytest
-import pytest_mock
 import yaml
 
 from esmvalcore._recipe import to_datasets
@@ -10,6 +12,9 @@
 from esmvalcore.exceptions import RecipeError
 from esmvalcore.local import LocalFile
 
+if TYPE_CHECKING:
+    import pytest_mock
+
 
 def test_from_recipe(session):
     recipe_txt = textwrap.dedent("""
diff --git a/tests/unit/task/test_taskset.py b/tests/unit/task/test_taskset.py
index 6e2dd9dccc..9f4c683c74 100644
--- a/tests/unit/task/test_taskset.py
+++ b/tests/unit/task/test_taskset.py
@@ -1,9 +1,16 @@
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
 import dask
 import pytest
 
 from esmvalcore import _task
 from esmvalcore.preprocessor import PreprocessingTask
 
+if TYPE_CHECKING:
+    from pytest_mock import MockerFixture
+
 
 @pytest.mark.parametrize(
     (
@@ -24,7 +31,7 @@
     ],
 )
 def test_taskset_get_dask_config(
-    mocker,
+    mocker: MockerFixture,
     max_parallel_tasks: int,
     available_cpu_cores: int,
     n_preproc_tasks: int,
@@ -53,7 +60,7 @@ def test_taskset_get_dask_config(
         assert config == {"num_workers": expected_workers}
 
 
-def test_taskset_get_dask_config_noop(mocker) -> None:
+def test_taskset_get_dask_config_noop(mocker: MockerFixture) -> None:
     tasks = _task.TaskSet()
 
     with dask.config.set({"num_workers": 4, "scheduler": "threads"}):
diff --git a/tests/unit/test_dataset.py b/tests/unit/test_dataset.py
index c1d320b258..63ebd22b91 100644
--- a/tests/unit/test_dataset.py
+++ b/tests/unit/test_dataset.py
@@ -1,8 +1,11 @@
+from __future__ import annotations
+
 import importlib.resources
 import textwrap
 from collections import defaultdict
 from functools import lru_cache
 from pathlib import Path
+from typing import TYPE_CHECKING
 
 import pyesgf
 import pytest
@@ -16,7 +19,9 @@
 from esmvalcore.dataset import Dataset
 from esmvalcore.esgf import ESGFFile
 from esmvalcore.exceptions import InputFilesNotFound, RecipeError
-from esmvalcore.typing import Facets
+
+if TYPE_CHECKING:
+    from esmvalcore.typing import Facets
 
 
 @lru_cache