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title: 'Tools (Function Calling)' sidebar_label: 'Tools' description: 'Tools YAML reference'

Tools define functions that can be invoked within the Spice runtime, either directly or by a language model (opens in a new tab) (LLMs). These tools provide access to different functionalities and can be customized in the tools section of spicepod.yaml.

tools

The tools section in your configuration specifies one or more tools available for use in the runtime.

Example:

name

A unique identifier for this tool.

from

Defines the source of the tool, or the specific built-in tool to customise. See Available Tools (opens in a new tab) for a list of available tools.

For MCP tools (opens in a new tab), the target is part of the from value itself, in the form mcp:<target>:

• mcp:<url> connects to an MCP server over Streamable HTTP, e.g. mcp:http://localhost:8090/v1/mcp.
• mcp:<command> runs a stdio-based MCP server as a subprocess, e.g. mcp:npx.

A bare from: mcp (without a :<target> suffix) is rejected when the spicepod is loaded.

description

Optional. A textual description of the tool's function.

params

Optional. A map of key-value pairs for additional parameters specific to the tool. For MCP tools these are mcp_args (stdio), and mcp_auth_token / mcp_headers (Streamable HTTP) — see MCP Tools (opens in a new tab). The MCP server address is set via from, not via params.

env

Optional. A map of key-value pairs of arbitrary environment variables to set when running the tool. Only useable if the tool requires a subprocess to run (e.g. MCP over stdio) .

dependsOn

Optional. A list of dependencies that must be available before this tool can be used.