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Tool Use (Function Calling)

Reviewed 19 July 2026Canonical definitionPart of: MCP & Agent Protocol Terms →

Tool use, or function calling, is the ability of an AI agent to call external tools, APIs, or functions to complete a task. In governed systems, every tool call should be scoped, authenticated, and logged.

§01 / QUESTIONSterm: Tool Use (Function Calling)
Questions

Common questions.

What is Tool Use (Function Calling)?

Tool use, or function calling, is the ability of an AI agent to call external tools, APIs, or functions to complete a task.

How does Tool Use (Function Calling) work?

In governed systems, every tool call should be scoped, authenticated, and logged.

Which terms are related to Tool Use (Function Calling)?

Closely related concepts include Agent Capability, AI Agent, Exfiltration via Agent, Agent Ecosystem. Each is defined in the Prefactor glossary.

§02 / RELATEDnext: where this fits
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Where this fits.

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