diff --git a/scripts/check_buildbot_system.py b/scripts/check_buildbot_system.py
new file mode 100644
index 00000000..f57ed418
--- /dev/null
+++ b/scripts/check_buildbot_system.py
@@ -0,0 +1,177 @@
+#!/usr/bin/env python3
+"""Check buildbot system directory for changes against local registry.
+
+Compares the live buildbot assets/system/.index against _data_dirs.yml
+entries using HTTP ETag headers for change detection.
+
+Usage:
+    python scripts/check_buildbot_system.py
+    python scripts/check_buildbot_system.py --update
+    python scripts/check_buildbot_system.py --json
+"""
+from __future__ import annotations
+
+import argparse
+import json
+import logging
+import subprocess
+import sys
+import urllib.error
+import urllib.parse
+import urllib.request
+from pathlib import Path
+
+log = logging.getLogger(__name__)
+
+BUILDBOT_SYSTEM_URL = "https://buildbot.libretro.com/assets/system/"
+INDEX_URL = BUILDBOT_SYSTEM_URL + ".index"
+USER_AGENT = "retrobios/1.0"
+REQUEST_TIMEOUT = 15
+
+DEFAULT_REGISTRY = "platforms/_data_dirs.yml"
+VERSIONS_FILE = "data/.versions.json"
+
+
+def fetch_index() -> set[str]:
+    """Fetch .index from buildbot, return set of ZIP filenames."""
+    req = urllib.request.Request(INDEX_URL, headers={"User-Agent": USER_AGENT})
+    with urllib.request.urlopen(req, timeout=REQUEST_TIMEOUT) as resp:
+        return {line.strip() for line in resp.read().decode().splitlines() if line.strip()}
+
+
+def load_tracked_entries(registry_path: str = DEFAULT_REGISTRY) -> dict[str, tuple[str, str]]:
+    """Load buildbot entries from _data_dirs.yml.
+
+    Returns {decoded_zip_name: (key, source_url)}.
+    """
+    try:
+        import yaml
+    except ImportError:
+        print("Error: PyYAML required", file=sys.stderr)
+        sys.exit(1)
+    with open(registry_path) as f:
+        data = yaml.safe_load(f) or {}
+    entries: dict[str, tuple[str, str]] = {}
+    for key, entry in data.get("data_directories", {}).items():
+        url = entry.get("source_url", "")
+        if "buildbot.libretro.com/assets/system" not in url:
+            continue
+        zip_name = urllib.parse.unquote(url.rsplit("/", 1)[-1])
+        entries[zip_name] = (key, url)
+    return entries
+
+
+def get_remote_etag(url: str) -> str | None:
+    """HEAD request to get ETag."""
+    try:
+        req = urllib.request.Request(url, method="HEAD",
+                                     headers={"User-Agent": USER_AGENT})
+        with urllib.request.urlopen(req, timeout=REQUEST_TIMEOUT) as resp:
+            return resp.headers.get("ETag") or resp.headers.get("Last-Modified") or ""
+    except (urllib.error.URLError, OSError):
+        return None
+
+
+def load_versions(versions_path: str = VERSIONS_FILE) -> dict:
+    """Load cached version/ETag data."""
+    path = Path(versions_path)
+    if not path.exists():
+        return {}
+    with open(path) as f:
+        return json.load(f)
+
+
+def check(registry_path: str = DEFAULT_REGISTRY) -> dict:
+    """Run the buildbot check. Returns structured report."""
+    try:
+        index_zips = fetch_index()
+    except (urllib.error.URLError, OSError) as exc:
+        log.warning("buildbot unreachable: %s", exc)
+        return {"error": str(exc), "entries": []}
+
+    tracked = load_tracked_entries(registry_path)
+    versions = load_versions()
+
+    buildbot_set = set(index_zips)
+    tracked_set = set(tracked.keys())
+
+    results: list[dict] = []
+
+    for z in sorted(buildbot_set - tracked_set):
+        results.append({"zip": z, "status": "NEW", "key": None})
+
+    for z in sorted(tracked_set - buildbot_set):
+        key, _ = tracked[z]
+        results.append({"zip": z, "status": "STALE", "key": key})
+
+    for z in sorted(tracked_set & buildbot_set):
+        key, url = tracked[z]
+        stored = versions.get(key, {}).get("sha", "")
+        remote = get_remote_etag(url)
+        if remote is None:
+            status = "UNKNOWN"
+        elif remote == stored:
+            status = "OK"
+        else:
+            status = "UPDATED"
+        results.append({"zip": z, "status": status, "key": key,
+                        "stored_etag": stored, "remote_etag": remote or ""})
+
+    return {"entries": results}
+
+
+def print_report(report: dict) -> None:
+    """Print human-readable report."""
+    if report.get("error"):
+        print(f"WARNING: {report['error']}")
+        return
+    entries = report["entries"]
+    print(f"Buildbot system check ({len(entries)} entries):")
+    for e in entries:
+        pad = 40 - len(e["zip"])
+        dots = "." * max(pad, 2)
+        print(f"  {e['zip']} {dots} {e['status']}")
+    counts: dict[str, int] = {}
+    for e in entries:
+        counts[e["status"]] = counts.get(e["status"], 0) + 1
+    parts = [f"{v} {k.lower()}" for k, v in sorted(counts.items())]
+    print(f"\nSummary: {', '.join(parts)}")
+
+
+def update_changed(report: dict) -> None:
+    """Refresh entries that have changed."""
+    for e in report.get("entries", []):
+        if e["status"] == "UPDATED" and e.get("key"):
+            log.info("refreshing %s ...", e["key"])
+            subprocess.run(
+                [sys.executable, "scripts/refresh_data_dirs.py",
+                 "--force", "--key", e["key"]],
+                check=False,
+            )
+
+
+def main() -> None:
+    logging.basicConfig(level=logging.INFO, format="%(message)s")
+    parser = argparse.ArgumentParser(
+        description="Check buildbot system directory for changes",
+    )
+    parser.add_argument("--update", action="store_true",
+                        help="Auto-refresh changed entries")
+    parser.add_argument("--json", action="store_true", dest="json_output",
+                        help="Machine-readable JSON output")
+    parser.add_argument("--registry", default=DEFAULT_REGISTRY)
+    args = parser.parse_args()
+
+    report = check(args.registry)
+
+    if args.json_output:
+        print(json.dumps(report, indent=2))
+    else:
+        print_report(report)
+
+    if args.update:
+        update_changed(report)
+
+
+if __name__ == "__main__":
+    main()