Add prompts to MCP server (#134619)

* Add prompts to MCP server

* Improve test coverage for get prompt error cases

homeassistant/components/mcp_server/server.py

@@ -50,6 +50,37 @@ async def create_server(
 
     server = Server("home-assistant")
 
+    @server.list_prompts()  # type: ignore[no-untyped-call, misc]
+    async def handle_list_prompts() -> list[types.Prompt]:
+        llm_api = await llm.async_get_api(hass, llm_api_id, llm_context)
+        return [
+            types.Prompt(
+                name=llm_api.api.name,
+                description=f"Default prompt for the Home Assistant LLM API {llm_api.api.name}",
+            )
+        ]
+
+    @server.get_prompt()  # type: ignore[no-untyped-call, misc]
+    async def handle_get_prompt(
+        name: str, arguments: dict[str, str] | None
+    ) -> types.GetPromptResult:
+        llm_api = await llm.async_get_api(hass, llm_api_id, llm_context)
+        if name != llm_api.api.name:
+            raise ValueError(f"Unknown prompt: {name}")
+
+        return types.GetPromptResult(
+            description=f"Default prompt for the Home Assistant LLM API {llm_api.api.name}",
+            messages=[
+                types.PromptMessage(
+                    role="assistant",
+                    content=types.TextContent(
+                        type="text",
+                        text=llm_api.api_prompt,
+                    ),
+                )
+            ],
+        )
+
     @server.list_tools()  # type: ignore[no-untyped-call, misc]
     async def list_tools() -> list[types.Tool]:
         """List available time tools."""

tests/components/mcp_server/test_http.py

@@ -10,6 +10,7 @@ import aiohttp
 import mcp
 import mcp.client.session
 import mcp.client.sse
+from mcp.shared.exceptions import McpError
 import pytest
 
 from homeassistant.components.conversation import DOMAIN as CONVERSATION_DOMAIN
@@ -354,3 +355,51 @@ async def test_mcp_tool_call_failed(
     assert len(result.content) == 1
     assert result.content[0].type == "text"
     assert "Error calling tool" in result.content[0].text
+
+
+async def test_prompt_list(
+    hass: HomeAssistant,
+    setup_integration: None,
+    mcp_sse_url: str,
+    hass_supervisor_access_token: str,
+) -> None:
+    """Test the list prompt endpoint."""
+
+    async with mcp_session(mcp_sse_url, hass_supervisor_access_token) as session:
+        result = await session.list_prompts()
+
+    assert len(result.prompts) == 1
+    prompt = result.prompts[0]
+    assert prompt.name == "Assist"
+    assert prompt.description == "Default prompt for the Home Assistant LLM API Assist"
+
+
+async def test_prompt_get(
+    hass: HomeAssistant,
+    setup_integration: None,
+    mcp_sse_url: str,
+    hass_supervisor_access_token: str,
+) -> None:
+    """Test the get prompt endpoint."""
+
+    async with mcp_session(mcp_sse_url, hass_supervisor_access_token) as session:
+        result = await session.get_prompt(name="Assist")
+
+    assert result.description == "Default prompt for the Home Assistant LLM API Assist"
+    assert len(result.messages) == 1
+    assert result.messages[0].role == "assistant"
+    assert result.messages[0].content.type == "text"
+    assert "When controlling Home Assistant" in result.messages[0].content.text
+
+
+async def test_get_unknwon_prompt(
+    hass: HomeAssistant,
+    setup_integration: None,
+    mcp_sse_url: str,
+    hass_supervisor_access_token: str,
+) -> None:
+    """Test the get prompt endpoint."""
+
+    async with mcp_session(mcp_sse_url, hass_supervisor_access_token) as session:
+        with pytest.raises(McpError):
+            await session.get_prompt(name="Unknown")