diff --git a/clients/deadline.py b/clients/deadline.py
index dac5a08..ae11918 100644
--- a/clients/deadline.py
+++ b/clients/deadline.py
@@ -29,6 +29,17 @@ def elapsed(self) -> float:
         """Return seconds since start; uncapped, may exceed timeout."""
         return self._clock.monotonic() - self._started_at
 
+    def fraction_used(self) -> float:
+        """Return elapsed/timeout clamped to [0, 1]; timeout==0 yields 1.0."""
+        if self._timeout == 0:
+            return 1.0
+        ratio = self.elapsed() / self._timeout
+        if ratio < 0:
+            return 0.0
+        if ratio > 1:
+            return 1.0
+        return ratio
+
     def remaining(self) -> float:
         """Return seconds left before the deadline (never negative)."""
         elapsed = self._clock.monotonic() - self._started_at
diff --git a/scenarios/cli.py b/scenarios/cli.py
index 97b2093..de409fc 100644
--- a/scenarios/cli.py
+++ b/scenarios/cli.py
@@ -69,6 +69,11 @@ def build_parser() -> argparse.ArgumentParser:
     )
 
     subparsers.add_parser("count", help="Print number of known scenarios")
+
+    has_parser = subparsers.add_parser(
+        "has", help="Check whether a scenario id is known"
+    )
+    has_parser.add_argument("scenario_id", help="Scenario id from the catalog")
     return parser
 
 
@@ -173,6 +178,12 @@ def main(argv: list[str] | None = None) -> int:
         print(len(known_scenario_ids()))
         return 0
 
+    if args.command == "has":
+        if args.scenario_id in known_scenario_ids():
+            return 0
+        print(f"unknown scenario: {args.scenario_id}", file=sys.stderr)
+        return 1
+
     return 1
 
 
diff --git a/tests/test_cli.py b/tests/test_cli.py
index b16c784..03fb37c 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -2,7 +2,7 @@
 import io
 import json
 import unittest
-from contextlib import redirect_stdout
+from contextlib import redirect_stderr, redirect_stdout
 from unittest.mock import patch
 
 from scenarios.cli import main
@@ -223,5 +223,18 @@ def test_ids_text_format_default_unchanged(self):
         self.assertEqual(lines, list(known_scenario_ids()))
 
 
+    def test_has_known_scenario_returns_zero(self):
+        code = main(["has", "retry"])
+        self.assertEqual(code, 0)
+
+    def test_has_unknown_scenario_returns_error(self):
+        err = io.StringIO()
+        with redirect_stderr(err):
+            code = main(["has", "missing"])
+        self.assertEqual(code, 1)
+        self.assertIn("unknown scenario: missing", err.getvalue())
+
+
+
 if __name__ == "__main__":
     unittest.main()
diff --git a/tests/test_deadline.py b/tests/test_deadline.py
index 572aebf..bd918ca 100644
--- a/tests/test_deadline.py
+++ b/tests/test_deadline.py
@@ -51,6 +51,22 @@ def test_elapsed_tracks_fake_clock_uncapped(self):
         self.assertAlmostEqual(deadline.elapsed(), 0.8)
         self.assertGreater(deadline.elapsed(), 0.5)
 
+    def test_fraction_used_clamped_to_unit_interval(self):
+        clock = FakeClock()
+        deadline = Deadline(clock, timeout=1.0)
+        self.assertAlmostEqual(deadline.fraction_used(), 0.0)
+        clock.sleep(0.25)
+        self.assertAlmostEqual(deadline.fraction_used(), 0.25)
+        clock.sleep(0.75)
+        self.assertAlmostEqual(deadline.fraction_used(), 1.0)
+        clock.sleep(0.5)
+        self.assertAlmostEqual(deadline.fraction_used(), 1.0)
+
+    def test_fraction_used_zero_timeout_is_one(self):
+        clock = FakeClock()
+        deadline = Deadline(clock, timeout=0.0)
+        self.assertEqual(deadline.fraction_used(), 1.0)
+
 
 if __name__ == "__main__":
     unittest.main()