Choose a tool

Tools let an agent act during or around a call. A tool can look up an order, transfer the caller, update another system, or process call data. A tool belongs to your organization. You can attach one tool to several agents and configure each attachment independently. Three separate choices define how a tool works: its source, its invocation, and its lifecycle.

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Choose the source

Choose where the work runs. The source does not determine when the tool runs.

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Choose the invocation

Invocation controls what starts the tool. You choose it on each attachment. The same API Request tool can be model-invoked on one agent and system-invoked on another. MCP tools are model-invoked. Only Custom Code, API Request, Current date and time, and User phone number support system invocation. See Run a tool on call events for the supported events and arguments.

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Follow the lifecycle

Most tools you author follow this lifecycle:

1. Create and edit the draft.
2. Run a successful test and resolve the publish checks.
3. Publish an immutable numbered version.
4. Attach that version to an agent.
5. Publish a new version and upgrade each attachment when you are ready.

An agent always uses the version pinned in its attachment. Editing or publishing a draft does not change a live agent. There are three exceptions:

• Ready-to-use tools already have published versions, so you only attach them.
• Send SMS requires Twilio credentials and a successful test before publishing.
• Activating an n8n workflow creates, tests, publishes, and attaches its tool.