diff --git a/profiling.py b/profiling.py
new file mode 100644
index 000000000..0d3c606f1
--- /dev/null
+++ b/profiling.py
@@ -0,0 +1,152 @@
+"""
+Temporary profiling utilities for comparing implementations.
+
+Usage in a management command or shell::
+
+    from documents.profiling import profile_block
+
+    with profile_block("new check_sanity"):
+        messages = check_sanity()
+
+    with profile_block("old check_sanity"):
+        messages = check_sanity_old()
+
+Drop this file when done.
+"""
+
+from __future__ import annotations
+
+import tracemalloc
+from contextlib import contextmanager
+from time import perf_counter
+from typing import TYPE_CHECKING
+from typing import Any
+
+if TYPE_CHECKING:
+    from collections.abc import Generator
+
+from django.db import connection
+from django.db import reset_queries
+from django.test.utils import override_settings
+
+
+@contextmanager
+def profile_block(label: str = "block") -> Generator[None, None, None]:
+    """Profile memory, wall time, and DB queries for a code block.
+
+    Prints a summary to stdout on exit. Requires no external packages.
+    Enables DEBUG temporarily to capture Django's query log.
+    """
+    tracemalloc.start()
+    snapshot_before = tracemalloc.take_snapshot()
+
+    with override_settings(DEBUG=True):
+        reset_queries()
+        start = perf_counter()
+
+        yield
+
+        elapsed = perf_counter() - start
+        queries = list(connection.queries)
+
+    snapshot_after = tracemalloc.take_snapshot()
+    _, peak = tracemalloc.get_traced_memory()
+    tracemalloc.stop()
+
+    # Compare snapshots for top allocations
+    stats = snapshot_after.compare_to(snapshot_before, "lineno")
+
+    query_time = sum(float(q["time"]) for q in queries)
+    mem_diff = sum(s.size_diff for s in stats)
+
+    print(f"\n{'=' * 60}")  # noqa: T201
+    print(f"  Profile: {label}")  # noqa: T201
+    print(f"{'=' * 60}")  # noqa: T201
+    print(f"  Wall time:    {elapsed:.4f}s")  # noqa: T201
+    print(f"  Queries:      {len(queries)} ({query_time:.4f}s)")  # noqa: T201
+    print(f"  Memory delta: {mem_diff / 1024:.1f} KiB")  # noqa: T201
+    print(f"  Peak memory:  {peak / 1024:.1f} KiB")  # noqa: T201
+    print("\n  Top 5 allocations:")  # noqa: T201
+    for stat in stats[:5]:
+        print(f"    {stat}")  # noqa: T201
+    print(f"{'=' * 60}\n")  # noqa: T201
+
+
+def profile_cpu(
+    fn,
+    *,
+    label: str,
+    top: int = 30,
+    sort: str = "cumtime",
+) -> tuple[Any, float]:
+    """Run *fn()* under cProfile, print stats, return (result, elapsed_s).
+
+    Args:
+        fn: Zero-argument callable to profile.
+        label: Human-readable label printed in the header.
+        top: Number of cProfile rows to print.
+        sort: cProfile sort key (default: cumulative time).
+
+    Returns:
+        ``(result, elapsed_s)`` where *result* is the return value of *fn()*.
+    """
+    import cProfile
+    import io
+    import pstats
+
+    pr = cProfile.Profile()
+    t0 = perf_counter()
+    pr.enable()
+    result = fn()
+    pr.disable()
+    elapsed = perf_counter() - t0
+
+    buf = io.StringIO()
+    ps = pstats.Stats(pr, stream=buf).sort_stats(sort)
+    ps.print_stats(top)
+
+    print(f"\n{'=' * 72}")  # noqa: T201
+    print(f"  {label}")  # noqa: T201
+    print(f"  wall time: {elapsed * 1000:.1f} ms")  # noqa: T201
+    print(f"{'=' * 72}")  # noqa: T201
+    print(buf.getvalue())  # noqa: T201
+
+    return result, elapsed
+
+
+def measure_memory(fn, *, label: str) -> tuple[Any, float, float]:
+    """Run *fn()* under tracemalloc, print allocation report.
+
+    Args:
+        fn: Zero-argument callable to profile.
+        label: Human-readable label printed in the header.
+
+    Returns:
+        ``(result, peak_kib, delta_kib)``.
+    """
+    tracemalloc.start()
+    snapshot_before = tracemalloc.take_snapshot()
+    t0 = perf_counter()
+    result = fn()
+    elapsed = perf_counter() - t0
+    snapshot_after = tracemalloc.take_snapshot()
+    _, peak = tracemalloc.get_traced_memory()
+    tracemalloc.stop()
+
+    stats = snapshot_after.compare_to(snapshot_before, "lineno")
+    delta_kib = sum(s.size_diff for s in stats) / 1024
+
+    print(f"\n{'=' * 72}")  # noqa: T201
+    print(f"  [memory] {label}")  # noqa: T201
+    print(f"  wall time:    {elapsed * 1000:.1f} ms")  # noqa: T201
+    print(f"  memory delta: {delta_kib:+.1f} KiB")  # noqa: T201
+    print(f"  peak traced:  {peak / 1024:.1f} KiB")  # noqa: T201
+    print(f"{'=' * 72}")  # noqa: T201
+    print("  Top allocation sites (by size_diff):")  # noqa: T201
+    for stat in stats[:20]:
+        if stat.size_diff != 0:
+            print(  # noqa: T201
+                f"    {stat.size_diff / 1024:+8.1f} KiB  {stat.traceback.format()[0]}",
+            )
+
+    return result, peak / 1024, delta_kib