What is function calling (tool calling)?

Given a set of tool definitions, the model can respond with a structured call — a function name and arguments matching a schema — instead of plain text. Your code executes it and returns the result, which the model uses to continue. This loop is what turns a chatbot into an agent that can act.

How reliably a model and framework handle tool calling is a major differentiator between agent stacks. Open standards like the Model Context Protocol standardise the tools themselves so they are reusable across clients.

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