Title: Why synchronous @mcp.tool definition is not supported for parallelism? · Issue #1646 · modelcontextprotocol/python-sdk · GitHub
Open Graph Title: Why synchronous @mcp.tool definition is not supported for parallelism? · Issue #1646 · modelcontextprotocol/python-sdk
X Title: Why synchronous @mcp.tool definition is not supported for parallelism? · Issue #1646 · modelcontextprotocol/python-sdk
Description: Question In mcp.server.fastmcp.utilities.func_metadata.FuncMetadata.call_fn_with_arg_validation if fn_is_async: return await fn(**arguments_parsed_dict) else: return fn(**arguments_parsed_dict) In FastMCP, if a tool is defined as a synch...
Open Graph Description: Question In mcp.server.fastmcp.utilities.func_metadata.FuncMetadata.call_fn_with_arg_validation if fn_is_async: return await fn(**arguments_parsed_dict) else: return fn(**arguments_parsed_dict) In ...
X Description: Question In mcp.server.fastmcp.utilities.func_metadata.FuncMetadata.call_fn_with_arg_validation if fn_is_async: return await fn(**arguments_parsed_dict) else: return fn(**arguments_parsed_dict) In ...
Opengraph URL: https://github.com/modelcontextprotocol/python-sdk/issues/1646
X: @github
Domain: github.com
{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Why synchronous @mcp.tool definition is not supported for parallelism?","articleBody":"### Question\n\nIn `mcp.server.fastmcp.utilities.func_metadata.FuncMetadata.call_fn_with_arg_validation`\n\n```python\nif fn_is_async:\n return await fn(**arguments_parsed_dict)\nelse:\n return fn(**arguments_parsed_dict)\n```\n\n\nIn FastMCP, if a tool is defined as a synchronous function, it will block the whole running loop instead of using to_thread().\n\nMay I know the consideration for it's different from FastAPI's concurrency model?\n\n### Additional Context\n\n_No response_","author":{"url":"https://github.com/MikeBai523","@type":"Person","name":"MikeBai523"},"datePublished":"2025-11-20T09:08:17.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/1646/python-sdk/issues/1646"}
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| og:image:alt | Question In mcp.server.fastmcp.utilities.func_metadata.FuncMetadata.call_fn_with_arg_validation if fn_is_async: return await fn(**arguments_parsed_dict) else: return fn(**arguments_parsed_dict) In ... |
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