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45 XP

Lesson 5 · 14 min

Function calling and tool use patterns

Use tool use to route decisions, call APIs, and build type-safe agent actions — from a single forced call to a full tool loop.

Tools as structured output

Tool use (function calling) is structured output taken further: instead of returning a JSON blob, the model selects which function to call and provides its arguments as a validated schema. This is the foundation of every agent system.