Unified TypeScript library for streaming, structured outputs, and agent loops across AI providers
Full evaluationGlossary · Updated Sep 2, 2026
Tool use (function calling)
A model's ability to call external functions, APIs, or tools by producing structured requests that software executes.
Definition
Tool use lets a model request actions such as searching the web, querying a database, running code, or sending a message, with the host application executing the call and returning results. It is the mechanism behind agents, plugins, and integrations, and it relies on clear tool descriptions and schemas.
Why it matters when choosing a tool
Tools that support function calling can act on your systems rather than only talk about them, which is what turns an assistant into an automation.
Where you will meet it
AI Agent & Chatbot Builders, AI Automation & Workflows, AI Coding & Development
Related terms
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