What is Tool calling?
Updated May 2026
Tool calling (or function calling) is when an AI model decides to call a real piece of code instead of just generating text — like checking a calendar before suggesting times.
Tool calling is what turns a language model into an agent. Without tools, the model can only generate text. With tools, it can read your real data, take real actions, and verify facts before answering.
A typical tool-calling loop: the visitor asks 'when can we meet next week?' → the AI decides to call check_availability → the tool returns real freebusy → the AI proposes real slots from that data.
Frequently asked questions
Is tool calling the same as function calling?
Yes. The terms are interchangeable. OpenAI popularized 'function calling'; Anthropic uses 'tool use'. They describe the same pattern.
Related terms
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