# Tool use (LLM)

**Source:** https://promtable.com/glossary/tool-use

> Tool use is the umbrella term for any LLM mechanism that lets the model invoke external functions, APIs, or services — function calling, code interpreter, MCP servers, browser actions.

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Tool use is the umbrella term for any LLM mechanism that lets the model invoke external functions, APIs, or services — function calling, code interpreter, MCP servers, browser actions.

Tool use turned LLMs into actors instead of just generators. The model emits a structured tool call (function name + arguments), the harness executes it, and the result flows back into the conversation. By 2026 every frontier model supports tool use natively; the engineering question is no longer whether but how to design tools well. Best practices: tight schemas, descriptive names, errors readable by the model, tight result payloads, fewer than ~30 tools per agent.

## When to use

- Any agent.
- Workflows where the model needs current data or destructive actions.

## Common mistakes

- Too many tools — mis-routing rates climb past ~30.
- Vague tool descriptions — the model uses them as documentation.
- Returning huge JSON dumps — context blows up.

## Related terms

- [function-calling](https://promtable.com/glossary/function-calling)
- [agent](https://promtable.com/glossary/agent)
- [mcp](https://promtable.com/glossary/mcp)
- [code-interpreter](https://promtable.com/glossary/code-interpreter)

*Last updated: 2026-06-01*
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Original page: https://promtable.com/glossary/tool-use
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