tool use
An LLM feature where the model can request execution of named functions (tools) and receive results before responding.
Definition
Tool use (Anthropic terminology) or function calling (OpenAI terminology) is the API feature that lets a model emit structured calls to predefined functions and read their results before producing a final answer. Tools are described with JSON Schema. It is the underlying primitive that makes agents possible; MCP standardises how tools are advertised across LLM clients.
When to use
See also
- agent — An LLM-driven program that plans, calls tools, observes results, and loops until it reaches a goal.
- MCP — Anthropic's open standard for connecting LLMs to external tools and data sources over JSON-RPC.
- JSON Schema — A JSON-based vocabulary for describing the shape, types, and constraints of JSON documents.