diff --git a/tool/compare_upstream.py b/tool/compare_upstream.py
new file mode 100644
index 00000000..3f14cffc
--- /dev/null
+++ b/tool/compare_upstream.py
@@ -0,0 +1,83 @@
+"""List local numpy-stubs that are older than NumPy."""
+
+import shutil
+import subprocess
+import sys
+import tempfile
+from pathlib import Path
+
+UPSTREAM_URL = "https://github.com/numpy/numpy.git"
+UPSTREAM_BRANCH = "maintenance/2.4.x"
+LOCAL_STUBS_ROOT = Path(__file__).resolve().parents[1] / "src" / "numpy-stubs"
+GIT_BIN = shutil.which("git") or "git"
+
+
+def _run_git(args: list[str], cwd: Path) -> str:
+    proc = subprocess.run(
+        [GIT_BIN, *args], cwd=cwd, check=False, capture_output=True, text=True
+    )
+    proc.check_returncode()
+    return proc.stdout.strip()
+
+
+def _latest_commit_ts(repo: Path, path: Path) -> int | None:
+    rel = path.relative_to(repo)
+    out = _run_git(["log", "-1", "--format=%ct", "--", str(rel)], cwd=repo)
+    return int(out)
+
+
+def _list_outdated(local_repo: Path, upstream_repo: Path) -> list[str]:
+    outdated: list[str] = []
+    for local_file in LOCAL_STUBS_ROOT.rglob("*.pyi"):
+        rel = local_file.relative_to(LOCAL_STUBS_ROOT)
+        upstream_file = upstream_repo / "numpy" / rel
+        if not upstream_file.exists():
+            continue
+
+        ts_local = _latest_commit_ts(local_repo, local_file)
+        ts_upstream = _latest_commit_ts(upstream_repo, upstream_file)
+        if ts_upstream is None:
+            continue
+
+        if ts_local is None or ts_upstream > ts_local:
+            if local_file.read_bytes() == upstream_file.read_bytes():
+                continue
+            outdated.append(str(rel))
+
+    return sorted(outdated)
+
+
+def _main() -> int:
+    local_repo = Path(__file__).resolve().parents[1]
+    if not LOCAL_STUBS_ROOT.is_dir():
+        print(f"Local stubs not found at {LOCAL_STUBS_ROOT}", file=sys.stderr)
+        return 2
+
+    with tempfile.TemporaryDirectory() as tmp:
+        tmp_path = Path(tmp)
+        print(f"Cloning upstream {UPSTREAM_BRANCH}...", file=sys.stderr)
+        _run_git(
+            [
+                "clone",
+                "--depth=1",
+                "--branch",
+                UPSTREAM_BRANCH,
+                UPSTREAM_URL,
+                str(tmp_path),
+            ],
+            cwd=tmp_path,
+        )
+        outdated = _list_outdated(local_repo, tmp_path)
+
+    if outdated:
+        print("Upstream is newer for:")
+        for rel in outdated:
+            print(f"https://github.com/numpy/numpy/blob/{UPSTREAM_BRANCH}/numpy/{rel}")
+    else:
+        print("All tracked stubs are up-to-date relative to upstream.")
+
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(_main())