Tool Use
ELI5 — The Vibe Check
Tool use is when an AI can call external functions, APIs, or programs to do things it can't do alone. The model can't actually calculate, browse the web, or query a database — but if you give it tools that do those things, it knows WHEN and HOW to use them. It's like giving a brain some hands: it can finally act on its ideas instead of just thinking about them.
Real Talk
Tool use (also called function calling) enables LLMs to invoke external functions, APIs, or services as part of generating a response. The model outputs structured tool calls with parameters, which the application executes and returns results to the model. This extends LLM capabilities beyond text generation to include computation, data retrieval, API interaction, and real-world actions.
When You'll Hear This
"The model uses tool calling to look up real-time stock prices." / "Enable tool use so the agent can actually create the Jira ticket."
Related Terms
Agentic AI
Agentic AI is when the AI doesn't just answer questions — it takes action.
AI Agent
An AI Agent is an AI system that can think, plan, and act on its own to accomplish a goal.
API (Application Programming Interface)
An API is like a menu at a restaurant. The kitchen (server) can do a bunch of things, but you can only order what's on the menu.
Function Calling
Function Calling is the OpenAI term for what Anthropic calls Tool Use — teaching the AI to call your code functions.
MCP Server
An MCP Server is like a plugin for your AI assistant.