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Tools are what turn a model into an agent. On its own a model answers only from what it already knows; tools let it search the live web, fetch a page, run code, or call into your own systems. You enable tools by listing them in the tools array, and within a single request the model runs an agentic loop — it reasons, calls a tool, observes the result, and repeats until it can answer.

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Three kinds of tools

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Built-in tools

Enable each by its type. Every tool has its own reference page for full settings, response shape, and pricing.

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Bring your own

MCP servers

Connect a remote MCP server with type: mcp and let the model call its tools automatically.

Custom functions

Declare a type: function tool with a JSON Schema and run the call on your side.