diff --git a/astromesh-adk/CHANGELOG.md b/astromesh-adk/CHANGELOG.md
index e19f90f8..5538049e 100644
--- a/astromesh-adk/CHANGELOG.md
+++ b/astromesh-adk/CHANGELOG.md
@@ -7,6 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+- `ADKRuntime._run_swarm` now raises a descriptive `ValueError` (`swarm team '<name>' has no entry_agent and no agents`) when an `AgentTeam` with the `swarm` pattern has neither `entry_agent` nor `agents`, instead of crashing with `IndexError` on `team.agents[0]` (`astromesh_adk/runner.py`)
+
 ## [0.1.9] - 2026-07-10
 
 ### Added
diff --git a/astromesh-adk/astromesh_adk/runner.py b/astromesh-adk/astromesh_adk/runner.py
index 97d56323..a9c8c0c0 100644
--- a/astromesh-adk/astromesh_adk/runner.py
+++ b/astromesh-adk/astromesh_adk/runner.py
@@ -438,6 +438,8 @@ async def delegating_tool_fn(name: str, args: dict):
         )
 
     async def _run_swarm(self, team, query, session_id, context) -> RunResult:
+        if team.entry_agent is None and not team.agents:
+            raise ValueError(f"swarm team {team.name!r} has no entry_agent and no agents")
         agents = {a.name: a for a in team.agents}
         entry = team.entry_agent or team.agents[0]
         tctx = TracingContext(entry.name, session_id)
diff --git a/astromesh-adk/tests/test_runner_local.py b/astromesh-adk/tests/test_runner_local.py
index 830d89b1..ae2e6cb9 100644
--- a/astromesh-adk/tests/test_runner_local.py
+++ b/astromesh-adk/tests/test_runner_local.py
@@ -318,3 +318,24 @@ async def on_after_run(self, ctx, result):
     result = await rt.run_class_agent(MyAgent(), "q", "s")
     assert result.answer == "cls-out"
     assert calls == ["before", "after"]
+
+
+@pytest.mark.asyncio
+async def test_run_team_swarm_returns_entry_answer():
+    rt = ADKRuntime(provider_factory=lambda p, m, c: FakeProvider(m, content="swarm-final"))
+    team = AgentTeam(
+        name="sw",
+        pattern="swarm",
+        agents=[_agent(name="a1", model="claude-x"), _agent(name="a2", model="gpt-y")],
+        entry_agent=_agent(name="entry", model="claude-x"),
+    )
+    result = await rt.run_team(team, "q", "s")
+    assert result.answer == "swarm-final"
+
+
+@pytest.mark.asyncio
+async def test_run_team_swarm_empty_team_raises_valueerror():
+    rt = ADKRuntime(provider_factory=lambda p, m, c: FakeProvider(m))
+    team = AgentTeam(name="empty", pattern="swarm", agents=[], entry_agent=None)
+    with pytest.raises(ValueError, match=r"swarm team 'empty' has no entry_agent and no agents"):
+        await rt.run_team(team, "q", "s")