# What Is Tool Use in AI Agents?

> Tool use (function calling) lets an AI agent invoke external capabilities — APIs, databases, search, code execution — instead of relying on text generation alone.

**Term:** Tool Use  
**Category:** Capabilities  
**Also known as:** function calling, tool calling, agent tools  
**Updated:** 2026-07-22  
**Canonical:** https://www.frameworkr.com/glossary/tool-use

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**Tool use** is how an AI agent interacts with the world beyond generating text. The model decides when to call an external capability — an API, database query, search engine, code interpreter, or messaging channel — and receives structured results it can reason about in the next loop iteration.

Without tools, an LLM can only talk. With tools, it can act.

## How tool use works

1. You define available tools with names, descriptions, and parameter schemas
2. The model receives the user goal and tool definitions in its context
3. During reasoning, the model outputs a structured tool call (name + arguments)
4. Your runtime executes the tool and returns the result
5. The model incorporates the result and decides the next step

This pattern is also called **function calling** when the tools are exposed as callable functions with typed parameters.

## Choosing the right tools

Tool selection is an architecture decision, not an implementation detail. Poor choices create compounding errors — an agent that can query any database will eventually query the wrong one. Good tool design:

- Gives each tool a **clear, narrow purpose**
- Uses **descriptive names** the model can match to intent
- Returns **structured, parseable** results
- Includes **validation** on inputs before execution

## Related reading

Browse the [AI agent tools catalog](/tools) for infrastructure mapped to each layer of an agent blueprint.

## Related terms

- [ai agent](https://www.frameworkr.com/glossary/ai-agent.md)
- [agent loop](https://www.frameworkr.com/glossary/agent-loop.md)
- [function calling](https://www.frameworkr.com/glossary/function-calling.md)
- [model context protocol](https://www.frameworkr.com/glossary/model-context-protocol.md)


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_Published by Frameworkr — https://www.frameworkr.com_