diff --git a/src/agent_rules_kit/cli.py b/src/agent_rules_kit/cli.py
index d4ebba7..a01e57e 100644
--- a/src/agent_rules_kit/cli.py
+++ b/src/agent_rules_kit/cli.py
@@ -3,9 +3,12 @@
 from __future__ import annotations
 
 import argparse
+import sys
 from collections.abc import Sequence
+from pathlib import Path
 
 from agent_rules_kit import __version__
+from agent_rules_kit.discovery import discover_instruction_files
 
 
 def build_parser() -> argparse.ArgumentParser:
@@ -19,6 +22,20 @@ def build_parser() -> argparse.ArgumentParser:
         action="store_true",
         help="Print the package version and exit.",
     )
+
+    subparsers = parser.add_subparsers(dest="command")
+
+    check_parser = subparsers.add_parser(
+        "check",
+        help="Discover supported agent instruction files in a repository.",
+    )
+    check_parser.add_argument(
+        "repository",
+        nargs="?",
+        default=".",
+        help="Repository root to inspect. Defaults to the current directory.",
+    )
+
     return parser
 
 
@@ -31,9 +48,32 @@ def main(argv: Sequence[str] | None = None) -> int:
         print(f"agent-rules-kit {__version__}")
         return 0
 
+    if args.command == "check":
+        return _run_check(Path(args.repository))
+
     parser.print_help()
     return 0
 
 
+def _run_check(repository_root: Path) -> int:
+    try:
+        instruction_files = discover_instruction_files(repository_root)
+    except ValueError as error:
+        print(f"ERROR: {error}", file=sys.stderr)
+        return 2
+
+    print(f"agent-rules-kit check: {repository_root}")
+
+    if not instruction_files:
+        print("No supported agent instruction files found.")
+        return 1
+
+    print(f"Found {len(instruction_files)} supported instruction file(s):")
+    for instruction_file in instruction_files:
+        print(f"- {instruction_file.path} [{instruction_file.kind.value}]")
+
+    return 0
+
+
 if __name__ == "__main__":
     raise SystemExit(main())
diff --git a/tests/test_cli.py b/tests/test_cli.py
index 4639c40..bfe2518 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -2,10 +2,13 @@
 
 import io
 import unittest
-from contextlib import redirect_stdout
+from contextlib import redirect_stderr, redirect_stdout
+from pathlib import Path
 
 from agent_rules_kit.cli import main
 
+FIXTURE_ROOT = Path(__file__).parent / "fixtures" / "repositories"
+
 
 class CliTests(unittest.TestCase):
     def test_version_flag_prints_version(self) -> None:
@@ -25,6 +28,45 @@ def test_help_is_default(self) -> None:
 
         self.assertEqual(exit_code, 0)
         self.assertIn("usage:", output.getvalue())
+        self.assertIn("check", output.getvalue())
+
+    def test_check_reports_discovered_instruction_files(self) -> None:
+        output = io.StringIO()
+
+        with redirect_stdout(output):
+            exit_code = main(["check", str(FIXTURE_ROOT / "multi-agent-overlap")])
+
+        text = output.getvalue()
+
+        self.assertEqual(exit_code, 0)
+        self.assertIn("Found 6 supported instruction file(s):", text)
+        self.assertIn("- AGENTS.md [agents]", text)
+        self.assertIn("- CLAUDE.md [claude]", text)
+        self.assertIn("- GEMINI.md [gemini]", text)
+        self.assertIn("- .cursor/rules/agent-rules.mdc [cursor-rule]", text)
+        self.assertIn("- .github/copilot-instructions.md [copilot]", text)
+        self.assertIn(
+            "- .github/instructions/agents.instructions.md [github-instruction]",
+            text,
+        )
+
+    def test_check_returns_one_when_no_instruction_files_are_found(self) -> None:
+        output = io.StringIO()
+
+        with redirect_stdout(output):
+            exit_code = main(["check", str(FIXTURE_ROOT / "empty-repo")])
+
+        self.assertEqual(exit_code, 1)
+        self.assertIn("No supported agent instruction files found.", output.getvalue())
+
+    def test_check_returns_two_for_invalid_repository_root(self) -> None:
+        output = io.StringIO()
+
+        with redirect_stderr(output):
+            exit_code = main(["check", str(FIXTURE_ROOT / "missing-repo")])
+
+        self.assertEqual(exit_code, 2)
+        self.assertIn("ERROR: repository root does not exist:", output.getvalue())
 
 
 if __name__ == "__main__":