Tool Calling

Also known as function calling

Tool calling — also called function calling — is the mechanism that lets a model request a structured action, like calling an API or running a query, instead of only generating text, with the calling application executing the action and returning the result. It's the primitive underneath every agent: an agent is essentially a model given a set of callable tools and a loop to call them in. Reliability here comes down to tight tool schemas and validating what the model actually asks for before executing it.

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