Tool Use — AI Glossary

Reference details

Related terms

• Function Calling
• AI Agent
• MCP (Model Context Protocol)
• Code Interpreter

Example: Where the model stops being able to guess

Ask a model for the 14th root of 892,371 and it will produce a confident, usually wrong number, because it is predicting digits. Give it a calculator tool and it emits pow(892371, 1/14), gets 2.534…, and reports that. The model did not get better at arithmetic; it stopped doing arithmetic.

Commonly confused with

Tool use is the capability; function calling is the interface that exposes it. A model can use tools through several mechanisms — a tool-calling API, MCP, or plain code generation that your runtime executes — and function calling is only the most common one.

When to use it

Reach for it when:

• Exactness matters and the model is unreliable: arithmetic, dates, lookups
• The information postdates training, or is private to your tenant
• The task has a real-world effect — sending, writing, booking

Reach for something else when:

• The model already knows the answer well; a tool adds latency and a failure mode
• You cannot authenticate or rate-limit the tool being called
• The tool's output is untrusted text that flows straight back into the prompt — that is the prompt-injection path

Referenced by

This term is used by the following ModelRefs references:

• function calling prompt
• react
• react
• plan and execute
• single tool agent
• multi tool router
• code execution agent
• learn agents
• learn mcp
• master langgraph
• anthropic builder path

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