diff --git a/clang-tools-extra/clang-tidy/tool/clang-tidy-alphabetical-order-check.py b/clang-tools-extra/clang-tidy/tool/clang-tidy-alphabetical-order-check.py
new file mode 100644
index 0000000000000..321663bb7d577
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/tool/clang-tidy-alphabetical-order-check.py
@@ -0,0 +1,301 @@
+#!/usr/bin/env python3
+
+"""
+Normalize clang-tidy docs with deterministic sorting for linting/tests.
+
+Subcommands:
+  - checks-list: Sort entries in docs/clang-tidy/checks/list.rst csv-table.
+  - release-notes: Sort key sections in docs/ReleaseNotes.rst and de-duplicate
+                   entries in "Changes in existing checks".
+
+Usage:
+  clang-tidy-alphabetical-order-check.py <subcommand> [-i <input rst>] [-o <output rst>] [--fix]
+
+Flags:
+  -i/--input   Input file.
+  -o/--output  Write normalized content here; omit to write to stdout.
+  --fix        Rewrite the input file in place. Cannot be combined with -o/--output.
+"""
+
+import argparse
+import io
+import os
+import re
+import sys
+from typing import List, Optional, Sequence, Tuple
+
+DOC_LABEL_RN_RE = re.compile(r":doc:`(?P<label>[^`<]+)\s*(?:<[^>]+>)?`")
+DOC_LINE_RE = re.compile(r"^\s*:doc:`(?P<label>[^`<]+?)\s*<[^>]+>`.*$")
+
+
+def script_dir() -> str:
+    return os.path.dirname(os.path.abspath(__file__))
+
+
+def read_text(path: str) -> List[str]:
+    with io.open(path, "r", encoding="utf-8") as f:
+        return f.read().splitlines(True)
+
+
+def write_text(path: str, content: str) -> None:
+    with io.open(path, "w", encoding="utf-8", newline="") as f:
+        f.write(content)
+
+
+def normalize_list_rst(lines: List[str]) -> str:
+    out: List[str] = []
+    i = 0
+    n = len(lines)
+    while i < n:
+        out.append(lines[i])
+        if lines[i].lstrip().startswith(".. csv-table::"):
+            i += 1
+            break
+        i += 1
+
+    while i < n and (lines[i].startswith(" ") or lines[i].strip() == ""):
+        if DOC_LINE_RE.match(lines[i]):
+            break
+        out.append(lines[i])
+        i += 1
+
+    entries: List[str] = []
+    while i < n and lines[i].startswith(" "):
+        if DOC_LINE_RE.match(lines[i]):
+            entries.append(lines[i])
+        else:
+            entries.append(lines[i])
+        i += 1
+
+    def key_for(line: str):
+        m = DOC_LINE_RE.match(line)
+        if not m:
+            return (1, "")
+        return (0, m.group("label"))
+
+    entries_sorted = sorted(entries, key=key_for)
+    out.extend(entries_sorted)
+    out.extend(lines[i:])
+
+    return "".join(out)
+
+
+def run_checks_list(
+    inp: Optional[str], out_path: Optional[str], fix: bool
+) -> int:
+    if not inp:
+        inp = os.path.normpath(
+            os.path.join(
+                script_dir(),
+                "..",
+                "..",
+                "docs",
+                "clang-tidy",
+                "checks",
+                "list.rst",
+            )
+        )
+    lines = read_text(inp)
+    normalized = normalize_list_rst(lines)
+    if fix and out_path:
+        sys.stderr.write("error: --fix cannot be used together with --output\n")
+        return 2
+    if fix:
+        original = "".join(lines)
+        if original != normalized:
+            write_text(inp, normalized)
+        return 0
+    if out_path:
+        write_text(out_path, normalized)
+        return 0
+    sys.stdout.write(normalized)
+    return 0
+
+
+def find_heading(lines: Sequence[str], title: str) -> Optional[int]:
+    for i in range(len(lines) - 1):
+        if lines[i].rstrip("\n") == title:
+            underline = lines[i + 1].rstrip("\n")
+            if (
+                underline
+                and set(underline) == {"^"}
+                and len(underline) >= len(title)
+            ):
+                return i
+    return None
+
+
+def extract_label(text: str) -> str:
+    m = DOC_LABEL_RN_RE.search(text)
+    return m.group("label") if m else text
+
+
+def is_bullet_start(line: str) -> bool:
+    return line.startswith("- ")
+
+
+def collect_bullet_blocks(
+    lines: Sequence[str], start: int, end: int
+) -> Tuple[List[str], List[Tuple[str, List[str]]], List[str]]:
+    i = start
+    n = end
+    first_bullet = i
+    while first_bullet < n and not is_bullet_start(lines[first_bullet]):
+        first_bullet += 1
+    prefix = list(lines[i:first_bullet])
+
+    blocks: List[Tuple[str, List[str]]] = []
+    i = first_bullet
+    while i < n:
+        if not is_bullet_start(lines[i]):
+            break
+        bstart = i
+        i += 1
+        while i < n and not is_bullet_start(lines[i]):
+            if (
+                i + 1 < n
+                and set(lines[i + 1].rstrip("\n")) == {"^"}
+                and lines[i].strip()
+            ):
+                break
+            i += 1
+        block = list(lines[bstart:i])
+        key = extract_label(block[0])
+        blocks.append((key, block))
+
+    suffix = list(lines[i:n])
+    return prefix, blocks, suffix
+
+
+def sort_and_dedup_blocks(
+    blocks: List[Tuple[str, List[str]]], dedup: bool = False
+) -> List[List[str]]:
+    seen = set()
+    filtered: List[Tuple[str, List[str]]] = []
+    for key, block in blocks:
+        if dedup:
+            if key in seen:
+                continue
+            seen.add(key)
+        filtered.append((key, block))
+    filtered.sort(key=lambda kb: kb[0])
+    return [b for _, b in filtered]
+
+
+def normalize_release_notes(lines: List[str]) -> str:
+    sections = [
+        ("New checks", False),
+        ("New check aliases", False),
+        ("Changes in existing checks", True),
+    ]
+
+    out = list(lines)
+
+    for idx in range(len(sections) - 1, -1, -1):
+        title, dedup = sections[idx]
+        h_start = find_heading(out, title)
+
+        if h_start is None:
+            continue
+
+        sec_start = h_start + 2
+
+        if idx + 1 < len(sections):
+            next_title = sections[idx + 1][0]
+            h_end = find_heading(out, next_title)
+            if h_end is None:
+                h_end = sec_start
+                while h_end + 1 < len(out):
+                    if out[h_end].strip() and set(
+                        out[h_end + 1].rstrip("\n")
+                    ) == {"^"}:
+                        break
+                    h_end += 1
+            sec_end = h_end
+        else:
+            h_end = sec_start
+            while h_end + 1 < len(out):
+                if out[h_end].strip() and set(out[h_end + 1].rstrip("\n")) == {
+                    "^"
+                }:
+                    break
+                h_end += 1
+            sec_end = h_end
+
+        prefix, blocks, suffix = collect_bullet_blocks(out, sec_start, sec_end)
+        sorted_blocks = sort_and_dedup_blocks(blocks, dedup=dedup)
+
+        new_section: List[str] = []
+        new_section.extend(prefix)
+        for i_b, b in enumerate(sorted_blocks):
+            if i_b > 0 and (
+                not new_section
+                or (new_section and new_section[-1].strip() != "")
+            ):
+                new_section.append("\n")
+            new_section.extend(b)
+        new_section.extend(suffix)
+
+        out = out[:sec_start] + new_section + out[sec_end:]
+
+    return "".join(out)
+
+
+def run_release_notes(
+    inp: Optional[str], out_path: Optional[str], fix: bool
+) -> int:
+    if not inp:
+        inp = os.path.normpath(
+            os.path.join(script_dir(), "..", "..", "docs", "ReleaseNotes.rst")
+        )
+    lines = read_text(inp)
+    normalized = normalize_release_notes(lines)
+    if fix and out_path:
+        sys.stderr.write("error: --fix cannot be used together with --output\n")
+        return 2
+    if fix:
+        original = "".join(lines)
+        if original != normalized:
+            write_text(inp, normalized)
+        return 0
+    if out_path:
+        write_text(out_path, normalized)
+        return 0
+    sys.stdout.write(normalized)
+    return 0
+
+
+def main(argv: List[str]) -> int:
+    ap = argparse.ArgumentParser()
+    sub = ap.add_subparsers(dest="cmd", required=True)
+
+    ap_checks = sub.add_parser(
+        "checks-list", help="normalize clang-tidy checks list.rst"
+    )
+    ap_checks.add_argument("-i", "--input", dest="inp", default=None)
+    ap_checks.add_argument("-o", "--output", dest="out", default=None)
+    ap_checks.add_argument(
+        "--fix", action="store_true", help="rewrite the input file in place"
+    )
+
+    ap_rn = sub.add_parser(
+        "release-notes", help="normalize ReleaseNotes.rst sections"
+    )
+    ap_rn.add_argument("-i", "--input", dest="inp", default=None)
+    ap_rn.add_argument("-o", "--output", dest="out", default=None)
+    ap_rn.add_argument(
+        "--fix", action="store_true", help="rewrite the input file in place"
+    )
+
+    args = ap.parse_args(argv)
+
+    if args.cmd == "checks-list":
+        return run_checks_list(args.inp, args.out, args.fix)
+    if args.cmd == "release-notes":
+        return run_release_notes(args.inp, args.out, args.fix)
+
+    ap.error("unknown command")
+
+
+if __name__ == "__main__":
+    main(sys.argv[1:])
diff --git a/clang-tools-extra/test/clang-tidy/infrastructure/alphabetical-order.cpp b/clang-tools-extra/test/clang-tidy/infrastructure/alphabetical-order.cpp
new file mode 100644
index 0000000000000..4a2598b93942b
--- /dev/null
+++ b/clang-tools-extra/test/clang-tidy/infrastructure/alphabetical-order.cpp
@@ -0,0 +1,6 @@
+// RUN: %python %S/../../../clang-tidy/tool/clang-tidy-alphabetical-order-check.py checks-list -i %S/../../../docs/clang-tidy/checks/list.rst -o %t.list
+// RUN: diff --strip-trailing-cr %t.list \
+// RUN:   %S/../../../docs/clang-tidy/checks/list.rst
+
+// RUN: %python %S/../../../clang-tidy/tool/clang-tidy-alphabetical-order-check.py release-notes -i %S/../../../docs/ReleaseNotes.rst -o %t.rn
+// RUN: diff --strip-trailing-cr %t.rn %S/../../../docs/ReleaseNotes.rst
diff --git a/clang-tools-extra/test/lit.cfg.py b/clang-tools-extra/test/lit.cfg.py
index c1da37d61bd61..c39ea29329674 100644
--- a/clang-tools-extra/test/lit.cfg.py
+++ b/clang-tools-extra/test/lit.cfg.py
@@ -57,6 +57,7 @@
 if config.clang_tidy_custom_check:
     config.available_features.add("custom-check")
 python_exec = shlex.quote(config.python_executable)
+config.substitutions.append(("%python", python_exec))
 check_clang_tidy = os.path.join(
     config.test_source_root, "clang-tidy", "check_clang_tidy.py"
 )