diff --git a/scripts/chatgpt-check-offset-diff.py b/scripts/chatgpt-check-offset-diff.py
new file mode 100644
index 0000000..c1cf230
--- /dev/null
+++ b/scripts/chatgpt-check-offset-diff.py
@@ -0,0 +1,118 @@
+#!/usr/bin/env python3
+
+from pathlib import Path
+from PIL import Image, ImageChops
+import argparse
+import re
+
+def load_rgb(path: Path) -> Image.Image:
+    return Image.open(path).convert("RGB")
+
+def mse(img: Image.Image) -> float:
+    hist = img.histogram()
+    sq = sum(v * ((i % 256) ** 2) for i, v in enumerate(hist))
+    return sq / (img.width * img.height * 3)
+
+def crop_pair(expected, actual, shift):
+    # shift > 0 means actual content is lower than expected.
+    w = min(expected.width, actual.width)
+
+    if shift >= 0:
+        e_box = (0, 0, w, min(expected.height, actual.height - shift))
+        a_box = (0, shift, w, shift + (e_box[3] - e_box[1]))
+    else:
+        s = -shift
+        a_box = (0, 0, w, min(actual.height, expected.height - s))
+        e_box = (0, s, w, s + (a_box[3] - a_box[1]))
+
+    return expected.crop(e_box), actual.crop(a_box)
+
+def best_vertical_shift(expected, actual, max_shift=100):
+    best = None
+
+    for shift in range(18, 19):
+        e, a = crop_pair(expected, actual, shift)
+        if e.height <= 0:
+            continue
+
+        score = mse(ImageChops.difference(e, a))
+        if best is None or score < best[1]:
+            best = (shift, score)
+
+    return best
+
+def changed_until_y(expected, actual, threshold=5, min_changed_pixels=10):
+    diff = ImageChops.difference(expected, actual)
+    last_changed = None
+
+    for y in range(diff.height):
+        row = diff.crop((0, y, diff.width, y + 1)).convert("L")
+        changed = sum(1 for px in row.getdata() if px > threshold)
+
+        if changed >= min_changed_pixels:
+            last_changed = y
+
+    return {
+        "last_changed_y": last_changed,
+        "clean_after_y": 0 if last_changed is None else last_changed + 1,
+    }
+
+def find_pairs(root: Path):
+    expected_files = sorted(root.rglob("*-expected.png"))
+
+    for expected in expected_files:
+        actual = expected.with_name(
+            expected.name.replace("-expected.png", "-actual.png")
+        )
+        if actual.exists():
+            yield expected, actual
+
+def main():
+    ap = argparse.ArgumentParser()
+    ap.add_argument("root", type=Path, nargs="?", default=Path("test-results"))
+    ap.add_argument("--max-shift", type=int, default=100)
+    ap.add_argument("--make-diffs", action="store_true")
+    args = ap.parse_args()
+
+    failed = False
+
+    for expected_path, actual_path in find_pairs(args.root):
+        expected = load_rgb(expected_path)
+        actual = load_rgb(actual_path)
+
+        raw_score = mse(ImageChops.difference(
+            expected.crop((0, 0, min(expected.width, actual.width), min(expected.height, actual.height))),
+            actual.crop((0, 0, min(expected.width, actual.width), min(expected.height, actual.height))),
+        ))
+
+        shift, shifted_score = best_vertical_shift(
+            expected, actual, max_shift=args.max_shift
+        )
+
+        status = "OK" if shifted_score < raw_score * 0.05 else "CHECK"
+        if status == "CHECK":
+            failed = True
+
+        rel = expected_path.relative_to(args.root)
+        print(f"{status} {rel}")
+        print(f"  expected: {expected.size}, actual: {actual.size}")
+        print(f"  best shift: {shift:+d}px")
+        print(f"  raw mse:     {raw_score:.3f}")
+        print(f"  shifted mse: {shifted_score:.3f}")
+
+        if args.make_diffs:
+            e, a = crop_pair(expected, actual, shift)
+            change_info = changed_until_y(e, a, threshold=2)
+            print(f"  last changed y after shift: {change_info['last_changed_y']}")
+            print(f"  clean after y after shift:  {change_info['clean_after_y']}")
+            diff = ImageChops.difference(e, a)
+            out = expected_path.with_name(
+                expected_path.name.replace("-expected.png", f"-shift-{shift:+d}-diff.png")
+            )
+            diff.save(out)
+            print(f"  wrote: {out}")
+
+    raise SystemExit(1 if failed else 0)
+
+if __name__ == "__main__":
+    main()