diff --git a/src/tests/test_tool_metadata.py b/src/tests/test_tool_metadata.py
index 3be8832..1902b7c 100644
--- a/src/tests/test_tool_metadata.py
+++ b/src/tests/test_tool_metadata.py
@@ -79,3 +79,22 @@ def test_server_advertises_codealive_version_and_compact_instructions():
     assert len(mcp.instructions.split()) <= 150
     assert "DISCOVER → SEARCH → READ → EXPAND" in mcp.instructions
     assert "chat only when the user explicitly requests" in mcp.instructions.lower()
+
+@pytest.mark.asyncio
+async def test_relationships_description_states_the_call_site_contract():
+    """The three call-site rules are only enforceable through the tool description: the backend can
+    omit positions for a repository indexed before call sites shipped, and a model that reads a
+    missing position as "no call" draws the opposite conclusion from the truth."""
+    # Arrange / Act
+    async with Client(mcp) as client:
+        tools = await client.list_tools()
+
+    # Assert
+    description = {tool.name: tool for tool in tools}["get_artifact_relationships"].description
+    assert description is not None
+    assert "call_sites" in description
+    assert "call_site_count" in description
+    # Missing position means "not indexed yet", never "no call".
+    assert "never" in description.lower()
+    # No parameter enables them, so the model must not go hunting for one.
+    assert "no parameter" in description.lower()
diff --git a/src/tools/artifact_relationships.py b/src/tools/artifact_relationships.py
index 545a2db..8327c76 100644
--- a/src/tools/artifact_relationships.py
+++ b/src/tools/artifact_relationships.py
@@ -33,6 +33,17 @@ async def get_artifact_relationships(
     This is a graph expansion tool, not a search tool. Use identifiers returned
     by semantic_search, grep_search, fetch_artifacts, read_file, or prior
     relationship results.
+
+    Call relationships also carry `call_sites` — each one a `position` written as
+    `path:line`, where the call is actually written — plus `call_site_count` for
+    how many exist in total. Read those exact lines instead of fetching the whole
+    caller. There is no parameter for this: positions come back whenever they are
+    known, so do not look for a flag. A call item with no `call_sites` means the position is not
+    indexed yet (the repository was indexed before call sites shipped, or that one
+    edge could not be located); it never means the call does not happen — the item
+    being listed at all is what says the call exists. A `confidence` on a site
+    appears only when the position is approximate; its absence means exact. For
+    incoming calls the file shown is the caller's file, not this artifact's.
     """
     tool_name = "get_artifact_relationships"
     require_text(identifier, tool_name, "identifier")