diff --git a/tools/metric_threshold_gate.py b/tools/metric_threshold_gate.py
new file mode 100644
index 0000000..071f0a9
--- /dev/null
+++ b/tools/metric_threshold_gate.py
@@ -0,0 +1,53 @@
+#!/usr/bin/env python3
+"""Fail a validation run when JSON metrics cross configured thresholds."""
+
+from __future__ import annotations
+
+import argparse
+import json
+from pathlib import Path
+from typing import Any
+
+
+def _records(path: Path) -> list[dict[str, Any]]:
+    data = json.loads(path.read_text(encoding="utf-8"))
+    if isinstance(data, dict):
+        data = data.get("results", data.get("records", []))
+    if not isinstance(data, list):
+        raise ValueError("metrics JSON must be a list or contain a results list")
+    return [item for item in data if isinstance(item, dict)]
+
+
+def evaluate(path: Path, metric: str, minimum: float | None, maximum: float | None) -> dict[str, Any]:
+    failures = []
+    for index, record in enumerate(_records(path)):
+        if metric not in record:
+            continue
+        value = float(record[metric])
+        if minimum is not None and value < minimum:
+            failures.append({"index": index, "metric": metric, "value": value, "reason": "below_minimum"})
+        if maximum is not None and value > maximum:
+            failures.append({"index": index, "metric": metric, "value": value, "reason": "above_maximum"})
+    return {"metric": metric, "failure_count": len(failures), "failures": failures}
+
+
+def main() -> int:
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("metrics", type=Path)
+    parser.add_argument("--metric", required=True)
+    parser.add_argument("--min", type=float, dest="minimum")
+    parser.add_argument("--max", type=float, dest="maximum")
+    parser.add_argument("--output", type=Path)
+    args = parser.parse_args()
+
+    report = evaluate(args.metrics, args.metric, args.minimum, args.maximum)
+    text = json.dumps(report, indent=2, ensure_ascii=False)
+    if args.output:
+        args.output.write_text(text + "\n", encoding="utf-8")
+    else:
+        print(text)
+    return 1 if report["failure_count"] else 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())
diff --git a/unit_test/test_metric_threshold_gate.py b/unit_test/test_metric_threshold_gate.py
new file mode 100644
index 0000000..8c66b21
--- /dev/null
+++ b/unit_test/test_metric_threshold_gate.py
@@ -0,0 +1,22 @@
+import json
+import tempfile
+import unittest
+from pathlib import Path
+
+from tools.metric_threshold_gate import evaluate
+
+
+class MetricThresholdGateTest(unittest.TestCase):
+    def test_reports_values_below_minimum(self):
+        with tempfile.TemporaryDirectory() as tmpdir:
+            path = Path(tmpdir) / "metrics.json"
+            path.write_text(json.dumps([{"latency_ms": 1.0}, {"latency_ms": 5.0}]), encoding="utf-8")
+
+            report = evaluate(path, "latency_ms", minimum=2.0, maximum=None)
+
+        self.assertEqual(report["failure_count"], 1)
+        self.assertEqual(report["failures"][0]["reason"], "below_minimum")
+
+
+if __name__ == "__main__":
+    unittest.main()