Tool Use & Function Calling

LLMs that can call external tools, APIs, databases, calculators, web browsers. Transforms LLMs from text generators into action-taking agents. Function calling is now supported by every major vendor, and the Model Context Protocol (MCP) has become the industry-standard way to connect models to tools. The substrate is the humble API, a documented endpoint the model can call, which is why giving a model an API and giving it a tool mean the same thing.

Key terms

Function callingAPI integrationMCPTool selectionAPIs

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