diff --git a/gate_v1_function/src/gate_v1_function/cli.py b/gate_v1_function/src/gate_v1_function/cli.py
new file mode 100644
index 0000000..58a28d3
--- /dev/null
+++ b/gate_v1_function/src/gate_v1_function/cli.py
@@ -0,0 +1,68 @@
+import argparse
+import json
+import sys
+from pathlib import Path
+
+from gate_v1_function.core import calculate_gate_decision
+
+
+def main() -> None:
+    """CLI entry point for Gate v1 Decision Function.
+
+    Parses CLI arguments and invokes calculate_gate_decision with given file paths.
+    Prints the resulting GateDecision (as JSON) to stdout.
+    """
+    parser = argparse.ArgumentParser(
+        description="Compute gate decision based on delta summary and delta cases."
+    )
+    parser.add_argument(
+        "--delta-summary",
+        required=True,
+        dest="delta_summary_path",
+        help="Path to delta_summary.json",
+    )
+    parser.add_argument(
+        "--delta-cases",
+        required=True,
+        dest="delta_cases_path",
+        help="Path to delta_cases.csv",
+    )
+    parser.add_argument(
+        "--whitelist",
+        required=False,
+        dest="unknown_whitelist_path",
+        help="Optional path to unknown_whitelist.json",
+    )
+
+    args = parser.parse_args()
+
+    # Basic input validation
+    delta_summary_path = Path(args.delta_summary_path)
+    delta_cases_path = Path(args.delta_cases_path)
+    unknown_whitelist_path = (Path(args.unknown_whitelist_path)
+                              if args.unknown_whitelist_path else None)
+
+    for p in [delta_summary_path, delta_cases_path]:
+        if not p.exists():
+            sys.stderr.write(f"Error: required file not found: {p}\n")
+            sys.exit(1)
+
+    # Call core function
+    try:
+        decision = calculate_gate_decision(
+            str(delta_summary_path), str(delta_cases_path),
+            str(unknown_whitelist_path) if unknown_whitelist_path else None
+        )
+    except Exception as exc:
+        sys.stderr.write(f"Error during gate calculation: {exc}\n")
+        sys.exit(2)
+
+    # Output decision JSON
+    print(json.dumps({
+        "decision": decision.decision,
+        "reasons": decision.reasons,
+    }, indent=2))
+
+
+if __name__ == "__main__":
+    main()