Glossary
Webhook
A webhook is an automatic message that a system sends to a defined web address as soon as a particular event occurs.
Unlike with an API query, the receiving system does not have to keep asking. It is notified when something happens. In AI telephony, typical events are: call ended, appointment booked, callback requested. The message contains the data of the event, mostly in JSON format, for example phone number, summary and the request that was recognised.
Webhooks make it possible to trigger processes without a ready-made integration: create an entry in the CRM, send a message in the team chat or start a workflow in an automation tool. For safe operation, the recipient should verify that the message really comes from the expected sender, for instance by a signature, and be able to deal with retries in case a message arrives twice.
In practice
In the sending system you enter an address to which events are sent and select the events you care about. On the receiving side there is either a small program of your own or an automation tool that accepts the message and processes it. To test, trigger an event, for example with a trial call, and look at the data that arrives. Acknowledge receipt quickly and do longer work afterwards. Many senders treat a slow response as a failure and send the same message again.
An example
A medical supply store wants every callback request to appear in the team chat immediately. It sets up a webhook for the event “call ended”. After each call a message with phone number, summary and request goes to an automation tool. The tool checks whether a callback was requested and posts to the customer advice channel who called, what it is about and by when the callback was promised. Nobody has to open a call list for that.
A common misunderstanding
Webhook and API are frequently confused. With an API you query or trigger something whenever you choose. A webhook reports by itself once something has happened. What gets underestimated is that a webhook’s address is publicly reachable. Without checking the signature, anyone who knows it could send invented events. And because messages can get lost or arrive twice, a process must not depend on each one arriving exactly once.
At Call0
Call0 offers webhooks and an API. Both are described in the documentation.
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As of: 12 October 2026