Add MCPServer.capabilities property.

Author: fennb

pydantic_ai_slim/pydantic_ai/_mcp.py

@@ -74,6 +74,31 @@ class ResourceTemplate(BaseResource):
     """URI template (RFC 6570) for constructing resource URIs."""
 
 
+@dataclass(repr=False, kw_only=True)
+class ServerCapabilities:
+    """Capabilities that an MCP server supports."""
+
+    experimental: list[str] | None = None
+    """Experimental, non-standard capabilities that the server supports."""
+
+    logging: bool = False
+    """Whether the server supports sending log messages to the client."""
+
+    prompts: bool = False
+    """Whether the server offers any prompt templates."""
+
+    resources: bool = False
+    """Whether the server offers any resources to read."""
+
+    tools: bool = False
+    """Whether the server offers any tools to call."""
+
+    completions: bool = False
+    """Whether the server offers autocompletion suggestions for prompts and resources."""
+
+    __repr__ = _utils.dataclasses_no_defaults_repr
+
+
 def map_from_mcp_params(params: mcp_types.CreateMessageRequestParams) -> list[messages.ModelMessage]:
     """Convert from MCP create message request parameters to pydantic-ai messages."""
     pai_messages: list[messages.ModelMessage] = []
@@ -217,3 +242,15 @@ def map_from_mcp_resource_template(mcp_template: mcp_types.ResourceTemplate) ->
         ),
         meta=mcp_template.meta,
     )
+
+
+def map_from_mcp_server_capabilities(mcp_capabilities: mcp_types.ServerCapabilities) -> ServerCapabilities:
+    """Convert from MCP ServerCapabilities to native Pydantic AI ServerCapabilities."""
+    return ServerCapabilities(
+        experimental=list(mcp_capabilities.experimental.keys()) if mcp_capabilities.experimental else None,
+        logging=mcp_capabilities.logging is not None,
+        prompts=mcp_capabilities.prompts is not None,
+        resources=mcp_capabilities.resources is not None,
+        tools=mcp_capabilities.tools is not None,
+        completions=mcp_capabilities.completions is not None,
+    )

pydantic_ai_slim/pydantic_ai/mcp.py

@@ -113,6 +113,7 @@ class MCPServer(AbstractToolset[Any], ABC):
     _read_stream: MemoryObjectReceiveStream[SessionMessage | Exception]
     _write_stream: MemoryObjectSendStream[SessionMessage]
     _server_info: mcp_types.Implementation
+    _server_capabilities: _mcp.ServerCapabilities
 
     def __init__(
         self,
@@ -191,6 +192,15 @@ def server_info(self) -> mcp_types.Implementation:
             )
         return self._server_info
 
+    @property
+    def capabilities(self) -> _mcp.ServerCapabilities:
+        """Access the capabilities advertised by the MCP server during initialization."""
+        if getattr(self, '_server_capabilities', None) is None:
+            raise AttributeError(
+                f'The `{self.__class__.__name__}.capabilities` is only instantiated after initialization.'
+            )
+        return self._server_capabilities
+
     async def list_tools(self) -> list[mcp_types.Tool]:
         """Retrieve tools that are currently active on the server.
 
@@ -374,6 +384,7 @@ async def __aenter__(self) -> Self:
                     with anyio.fail_after(self.timeout):
                         result = await self._client.initialize()
                         self._server_info = result.serverInfo
+                        self._server_capabilities = _mcp.map_from_mcp_server_capabilities(result.capabilities)
                         if log_level := self.log_level:
                             await self._client.set_logging_level(log_level)
 

tests/test_mcp.py

@@ -1568,3 +1568,18 @@ async def test_server_info(mcp_server: MCPServerStdio) -> None:
     async with mcp_server:
         assert mcp_server.server_info is not None
         assert mcp_server.server_info.name == 'Pydantic AI MCP Server'
+
+
+async def test_capabilities(mcp_server: MCPServerStdio) -> None:
+    with pytest.raises(
+        AttributeError, match='The `MCPServerStdio.capabilities` is only instantiated after initialization.'
+    ):
+        mcp_server.capabilities
+    async with mcp_server:
+        assert mcp_server.capabilities is not None
+        assert mcp_server.capabilities.resources is True
+        assert mcp_server.capabilities.tools is True
+        assert mcp_server.capabilities.prompts is True
+        assert mcp_server.capabilities.logging is True
+        assert mcp_server.capabilities.completions is False
+        assert mcp_server.capabilities.experimental is None