diff --git a/src/google/adk/cli/conformance/_conformance_test_google_llm.py b/src/google/adk/cli/conformance/_conformance_test_google_llm.py
index b1b86e06e0..374c0330e3 100644
--- a/src/google/adk/cli/conformance/_conformance_test_google_llm.py
+++ b/src/google/adk/cli/conformance/_conformance_test_google_llm.py
@@ -239,6 +239,13 @@ def __init__(
   ) -> None:
     super().__init__(**kwargs)
     recordings = config.get('_adk_replay_recordings')
+    if recordings is None:
+      raise ReplayVerificationError(
+          'Replay recordings were not loaded. The ADK web server must be'
+          ' started with the replay plugin, e.g. `adk web'
+          ' --extra_plugins=google.adk.cli.plugins.replay_plugin.ReplayPlugin`,'
+          ' for `adk conformance test` to work.'
+      )
     self._user_message_index = config.get('user_message_index')
     self._agent_name = config.get('agent_name')
     self._replay_index = config.get('current_replay_index')
diff --git a/tests/unittests/cli/conformance/test_conformance_test_google_llm.py b/tests/unittests/cli/conformance/test_conformance_test_google_llm.py
new file mode 100644
index 0000000000..a9c174e31c
--- /dev/null
+++ b/tests/unittests/cli/conformance/test_conformance_test_google_llm.py
@@ -0,0 +1,53 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Tests for _ConformanceTestGemini's handling of missing replay recordings."""
+
+from google.adk.cli.conformance._conformance_test_google_llm import _ConformanceTestGemini
+from google.adk.cli.conformance._conformance_test_google_llm import ReplayVerificationError
+from google.adk.cli.plugins.recordings_schema import Recordings
+import pytest
+
+
+def test_missing_recordings_raises_actionable_error():
+  """Replaying without the replay plugin loaded should fail clearly.
+
+  `config['_adk_replay_recordings']` is only populated by ReplayPlugin's
+  before_run_callback. If the server serving `adk conformance test` wasn't
+  started with that plugin, the key is absent and `config.get(...)` returns
+  None. Silently indexing into `None.recordings` used to raise a bare
+  AttributeError; it should now explain what's missing.
+  """
+  config = {
+      'user_message_index': 0,
+      'agent_name': 'root_agent',
+      'current_replay_index': 0,
+  }
+
+  with pytest.raises(ReplayVerificationError, match='ReplayPlugin'):
+    _ConformanceTestGemini(config=config)
+
+
+def test_present_recordings_does_not_raise():
+  """Sanity check: a properly loaded config constructs without error."""
+  config = {
+      '_adk_replay_recordings': Recordings(recordings=[]),
+      'user_message_index': 0,
+      'agent_name': 'root_agent',
+      'current_replay_index': 0,
+  }
+
+  model = _ConformanceTestGemini(config=config)
+
+  assert model._agent_llm_recordings == []