A capability of modern LLMs that allows them to generate structured requests to invoke specific functions or APIs. When an LLM determines that it needs to take an action — such as searching a database, calling an API, or performing a calculation — it outputs a structured function call with the appropriate parameters, which the host application then executes and returns results to the model.
Related Terms
Tool Use
The ability of an AI agent to interact with external systems, APIs, databases, and software tools to gather information or take actions in the real world. Tool use transforms LLMs from text generators into systems that can search the web, query databases, send emails, write code, and interact with any API.
AI Agent
An autonomous software system powered by a large language model (LLM) that can perceive its environment, make decisions, and take actions to achieve specific goals. Unlike simple chatbots, AI agents can use tools, access external data, maintain context across interactions, and chain multiple reasoning steps together.
MCP (Model Context Protocol)
An open protocol developed by Anthropic that standardizes how AI applications connect to external data sources and tools. MCP provides a universal interface for AI agents to access files, databases, APIs, and other systems — similar to how USB standardized peripheral connections.