8000 Clarification Needed: Fundamental Differences Between Function Calling and MCP · Issue #835 · modelcontextprotocol/python-sdk · GitHub
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Clarification Needed: Fundamental Differences Between Function Calling and MCP #835
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@Wuhall

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@Wuhall

​​Description:​​
Hi community,

I’m trying to deeply understand the distinction between OpenAI’s ​​Function Calling​​ and ​​Model Context Protocol (MCP)​​. While both involve structured data (JSON) interaction with the model, their purposes and workflows seem fundamentally different. Here’s my current understanding:

​​Function Calling​​
The model decides when to invoke external tools/APIs based on user input.
Output: Structured requests (e.g., {"function": "get_weather", "location": "Tokyo"}).
Use case: Dynamic action execution (e.g., calling an API, querying a database).
​​Model Context Protocol (MCP)​​
External systems inject structured context (e.g., session state, retrieved knowledge) into the model’s prompt.
Input: Predefined JSON format describing context (e.g., {"user_preferences": {"theme": "dark"}}).
Use case: Context-aware responses without model-initiated actions.
​​Key Confusion:​​

Is MCP more about passive context enrichment, while Function Calling is about active model-driven actions?
How do they complement each other in complex workflows (e.g., a chatbot using both context and API calls)?
Would love insights from anyone who has implemented both! Examples or architecture diagrams would be especially helpful.

​​Tags:​​ #function-calling #mcp #structured-data #integration

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