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Only list MCP tools once, not at every agent run step #3227

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Merged
merged 2 commits into from
Oct 22, 2025
Merged

Only list MCP tools once, not at every agent run step #3227

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0b9f2e1
Only list MCP tools once, not at every agent run step
DouweM Oct 22, 2025
0281740
Merge branch 'main' into mcp-list-tools-once
DouweM Oct 22, 2025
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11 changes: 7 additions & 4 deletions pydantic_ai_slim/pydantic_ai/mcp.py
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Original file line number Diff line number Diff line change
Expand Up @@ -113,6 +113,7 @@ class MCPServer(AbstractToolset[Any], ABC):
_read_stream: MemoryObjectReceiveStream[SessionMessage | Exception]
_write_stream: MemoryObjectSendStream[SessionMessage]
_server_info: mcp_types.Implementation
_tools: list[mcp_types.Tool] | None

def __init__(
self,
Expand Down Expand Up @@ -148,6 +149,7 @@ def __post_init__(self):
self._enter_lock = Lock()
self._running_count = 0
self._exit_stack = None
self._tools = None

@abstractmethod
@asynccontextmanager
Expand Down Expand Up @@ -194,13 +196,14 @@ def server_info(self) -> mcp_types.Implementation:
async def list_tools(self) -> list[mcp_types.Tool]:
"""Retrieve tools that are currently active on the server.

Note:
- We don't cache tools as they might change.
- We also don't subscribe to the server to avoid complexity.
Note that we don't subscribe to the server to avoid complexity.
"""
if self._tools is not None:
return self._tools
async with self: # Ensure server is running
result = await self._client.list_tools()
return result.tools
self._tools = result.tools
return self._tools

async def direct_call_tool(
self,
Expand Down