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A webhook tool is powerful and it is also an afternoon of work: an endpoint to write, somewhere to host it, a secret to verify. That work sits between “I made an agent” and “my agent booked a meeting”, and it is where most people stop. Library skills have no webhook. Zavu runs them. You add one from the agent’s Tools tab and it works on a phone call and in a thread, with the same behaviour on both.

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What is available

Library skills are added from the dashboard. The REST API and the CLI manage webhook tools, which is what zavu agents tools list shows.

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Connect a calendar

Both booking skills read one calendar per project. Open the agent’s Tools tab, then Library, then Connect one on either skill.

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Cal.com

You need two things from Cal.com:
  • an API key — Settings, then Developer, then API keys
  • the event type id — the number in the event type’s own URL
Cal.com keeps its own availability rules, buffers and limits. Zavu asks it for open slots and books them; it never second-guesses them.

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Google Calendar

Connecting is an OAuth grant. Zavu asks for two scopes: read your busy times, and write the events the agent books. Nothing else. Your working window is yours to set, because Google has no concept of one: the agent will only offer times inside the days and hours you configure.
Times are resolved in the time zone on the connection, and the agent always says the zone out loud. Set it to the business’s zone, not yours, if they differ.

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What the agent does with them

check_availability returns open slots and the zone they are in. book_meeting takes one of those slots plus a name and an email. The important part is what happens when a booking is not accepted. A Cal.com event type that requires confirmation answers pending, which is not a booking. The skill tells the agent exactly that, and the agent says the time is held but not confirmed. An agent that reports pending as booked sends someone to a meeting that may never exist, which is the worst outcome available on that call. The same rule covers the rest: no calendar connected, a slot in the past, a calendar that cannot be reached. Each one comes back as something the agent can say, never as a silent success.

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Draft a custom tool from a description

For anything the library does not cover you still write a webhook, but you do not have to write the schema. In Tools, Custom tool, describe what it should do:
You get a name, a description written for the model, and a parameter schema, all filled into the form for you to review before saving. Whatever it changed to make the definition valid is listed underneath: a renamed parameter, a nested object flattened to text, a required field dropped because it was not declared. It does not invent the endpoint. Where the tool sends its arguments is the one thing only you know, and a guessed URL produces a tool that looks finished and does nothing.

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Where to go next

Webhook tools

Build a tool against your own endpoint.

Voice agents

Where skills matter most, because the caller is waiting.