diff --git a/libc/utils/hdrgen/hdrgen/header.py b/libc/utils/hdrgen/hdrgen/header.py
index 715d4b7c9b7ed..558ee58469207 100644
--- a/libc/utils/hdrgen/hdrgen/header.py
+++ b/libc/utils/hdrgen/hdrgen/header.py
@@ -35,6 +35,13 @@
 
 COMMON_HEADER = PurePosixPath("__llvm-libc-common.h")
 
+# These "attributes" are known macros defined in COMMON_HEADER.
+# Others are found in "llvm-libc-macros/{name}.h".
+COMMON_ATTRIBUTES = {
+    "_Noreturn",
+    "_Returns_twice",
+}
+
 # All the canonical identifiers are in lowercase for easy maintenance.
 # This maps them to the pretty descriptions to generate in header comments.
 LIBRARY_DESCRIPTIONS = {
@@ -50,9 +57,7 @@
 HEADER_TEMPLATE = """\
 //===-- {library} header <{header}> --===//
 //
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+{license_lines}
 //
 //===---------------------------------------------------------------------===//
 
@@ -64,6 +69,12 @@
 #endif // {guard}
 """
 
+LLVM_LICENSE_TEXT = [
+    "Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.",
+    "See https://llvm.org/LICENSE.txt for license information.",
+    "SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception",
+]
+
 
 class HeaderFile:
     def __init__(self, name):
@@ -74,8 +85,10 @@ def __init__(self, name):
         self.enumerations = []
         self.objects = []
         self.functions = []
+        self.extra_standards = {}
         self.standards = []
         self.merge_yaml_files = []
+        self.license_text = []
 
     def add_macro(self, macro):
         self.macros.append(macro)
@@ -98,6 +111,11 @@ def merge(self, other):
         self.enumerations = sorted(set(self.enumerations) | set(other.enumerations))
         self.objects = sorted(set(self.objects) | set(other.objects))
         self.functions = sorted(set(self.functions) | set(other.functions))
+        self.extra_standards |= other.extra_standards
+        if self.license_text:
+            assert not other.license_text, "only one `license_text` allowed"
+        else:
+            self.license_text = other.license_text
 
     def all_types(self):
         return reduce(
@@ -106,6 +124,13 @@ def all_types(self):
             set(self.types),
         )
 
+    def all_attributes(self):
+        return reduce(
+            lambda a, b: a | b,
+            [set(f.attributes) for f in self.functions],
+            set(),
+        )
+
     def all_standards(self):
         # FIXME: Only functions have the "standard" field, but all the entity
         # types should have one too.
@@ -114,16 +139,24 @@ def all_standards(self):
         )
 
     def includes(self):
-        return {
-            PurePosixPath("llvm-libc-macros") / macro.header
-            for macro in self.macros
-            if macro.header is not None
-        } | {
-            COMPILER_HEADER_TYPES.get(
-                typ.type_name, PurePosixPath("llvm-libc-types") / f"{typ.type_name}.h"
-            )
-            for typ in self.all_types()
-        }
+        return (
+            {
+                PurePosixPath("llvm-libc-macros") / macro.header
+                for macro in self.macros
+                if macro.header is not None
+            }
+            | {
+                COMPILER_HEADER_TYPES.get(
+                    typ.type_name,
+                    PurePosixPath("llvm-libc-types") / f"{typ.type_name}.h",
+                )
+                for typ in self.all_types()
+            }
+            | {
+                PurePosixPath("llvm-libc-macros") / f"{attr}.h"
+                for attr in self.all_attributes() - COMMON_ATTRIBUTES
+            }
+        )
 
     def header_guard(self):
         return "_LLVM_LIBC_" + "_".join(
@@ -131,24 +164,29 @@ def header_guard(self):
         )
 
     def library_description(self):
+        descriptions = LIBRARY_DESCRIPTIONS | self.extra_standards
         # If the header itself is in standard C, just call it that.
         if "stdc" in self.standards:
-            return LIBRARY_DESCRIPTIONS["stdc"]
+            return descriptions["stdc"]
         # If the header itself is in POSIX, just call it that.
         if "posix" in self.standards:
-            return LIBRARY_DESCRIPTIONS["posix"]
+            return descriptions["posix"]
         # Otherwise, consider the standards for each symbol as well.
         standards = self.all_standards()
         # Otherwise, it's described by all those that apply, but ignoring
         # "stdc" and "posix" since this is not a "stdc" or "posix" header.
         return " / ".join(
             sorted(
-                LIBRARY_DESCRIPTIONS[standard]
+                descriptions[standard]
                 for standard in standards
                 if standard not in {"stdc", "posix"}
             )
         )
 
+    def license_lines(self):
+        lines = self.license_text or LLVM_LICENSE_TEXT
+        return "\n".join([f"// {line}" for line in lines])
+
     def template(self, dir, files_read):
         if self.template_file is not None:
             # There's a custom template file, so just read it in and record
@@ -162,6 +200,7 @@ def template(self, dir, files_read):
             library=self.library_description(),
             header=self.name,
             guard=self.header_guard(),
+            license_lines=self.license_lines(),
         )
 
     def public_api(self):
diff --git a/libc/utils/hdrgen/hdrgen/yaml_to_classes.py b/libc/utils/hdrgen/hdrgen/yaml_to_classes.py
index ebe7781d449f7..9eddbe615cbba 100644
--- a/libc/utils/hdrgen/hdrgen/yaml_to_classes.py
+++ b/libc/utils/hdrgen/hdrgen/yaml_to_classes.py
@@ -37,6 +37,8 @@ def yaml_to_classes(yaml_data, header_class, entry_points=None):
     header = header_class(header_name)
     header.template_file = yaml_data.get("header_template")
     header.standards = yaml_data.get("standards", [])
+    header.extra_standards = yaml_data.get("extra_standards", {})
+    header.license_text = yaml_data.get("license_text", [])
     header.merge_yaml_files = yaml_data.get("merge_yaml_files", [])
 
     for macro_data in yaml_data.get("macros", []):
diff --git a/libc/utils/hdrgen/tests/expected_output/custom.h b/libc/utils/hdrgen/tests/expected_output/custom.h
new file mode 100644
index 0000000000000..5f9ed231490fd
--- /dev/null
+++ b/libc/utils/hdrgen/tests/expected_output/custom.h
@@ -0,0 +1,21 @@
+//===-- Wile E. Coyote header <custom.h> --===//
+//
+// Caveat emptor.
+// I never studied law.
+//
+//===---------------------------------------------------------------------===//
+
+#ifndef _LLVM_LIBC_CUSTOM_H
+#define _LLVM_LIBC_CUSTOM_H
+
+#include "__llvm-libc-common.h"
+#include "llvm-libc-types/meep.h"
+#include "llvm-libc-types/road.h"
+
+__BEGIN_C_DECLS
+
+road runner(meep, meep) __NOEXCEPT;
+
+__END_C_DECLS
+
+#endif // _LLVM_LIBC_CUSTOM_H
diff --git a/libc/utils/hdrgen/tests/expected_output/test_header.h b/libc/utils/hdrgen/tests/expected_output/test_header.h
index 748c09808c128..49112a353f7b6 100644
--- a/libc/utils/hdrgen/tests/expected_output/test_header.h
+++ b/libc/utils/hdrgen/tests/expected_output/test_header.h
@@ -12,6 +12,7 @@
 #include "__llvm-libc-common.h"
 #include "llvm-libc-macros/float16-macros.h"
 
+#include "llvm-libc-macros/CONST_FUNC_A.h"
 #include "llvm-libc-macros/test_more-macros.h"
 #include "llvm-libc-macros/test_small-macros.h"
 #include "llvm-libc-types/float128.h"
diff --git a/libc/utils/hdrgen/tests/expected_output/test_small.json b/libc/utils/hdrgen/tests/expected_output/test_small.json
index 9cc73d013a679..8502df23b9a41 100644
--- a/libc/utils/hdrgen/tests/expected_output/test_small.json
+++ b/libc/utils/hdrgen/tests/expected_output/test_small.json
@@ -4,6 +4,7 @@
     "standards": [],
     "includes": [
       "__llvm-libc-common.h",
+      "llvm-libc-macros/CONST_FUNC_A.h",
       "llvm-libc-macros/test_more-macros.h",
       "llvm-libc-macros/test_small-macros.h",
       "llvm-libc-types/float128.h",
diff --git a/libc/utils/hdrgen/tests/input/custom-common.yaml b/libc/utils/hdrgen/tests/input/custom-common.yaml
new file mode 100644
index 0000000000000..909a3ba5163a5
--- /dev/null
+++ b/libc/utils/hdrgen/tests/input/custom-common.yaml
@@ -0,0 +1,6 @@
+license_text:
+  - Caveat emptor.
+  - I never studied law.
+
+extra_standards:
+  acme: Wile E. Coyote
diff --git a/libc/utils/hdrgen/tests/input/custom.yaml b/libc/utils/hdrgen/tests/input/custom.yaml
new file mode 100644
index 0000000000000..7d3ff8ec421dd
--- /dev/null
+++ b/libc/utils/hdrgen/tests/input/custom.yaml
@@ -0,0 +1,13 @@
+merge_yaml_files:
+  - custom-common.yaml
+
+header: custom.h
+standards:
+  - acme
+
+functions:
+  - name: runner
+    return_type: road
+    arguments:
+      - type: meep
+      - type: meep
diff --git a/libc/utils/hdrgen/tests/test_integration.py b/libc/utils/hdrgen/tests/test_integration.py
index bf393d26a8101..c6e76d826a3a4 100644
--- a/libc/utils/hdrgen/tests/test_integration.py
+++ b/libc/utils/hdrgen/tests/test_integration.py
@@ -59,6 +59,13 @@ def test_generate_subdir_header(self):
         self.run_script(yaml_file, output_file)
         self.compare_files(output_file, expected_output_file)
 
+    def test_custom_license_and_standards(self):
+        yaml_file = self.source_dir / "input" / "custom.yaml"
+        expected_output_file = self.source_dir / "expected_output" / "custom.h"
+        output_file = self.output_dir / "custom.h"
+        self.run_script(yaml_file, output_file)
+        self.compare_files(output_file, expected_output_file)
+
     def test_generate_json(self):
         yaml_file = self.source_dir / "input/test_small.yaml"
         expected_output_file = self.source_dir / "expected_output/test_small.json"