# What is a webhook?

> A webhook is an HTTP message a system sends when something happens. How webhooks work, how they are secured and how they connect time tracking.

URL: https://timetracking.tech/glossary/webhook
Language: en
Last updated: 2026-10-24

**Definition:** A webhook is an automatic HTTP request that one system sends to a URL of another system as soon as a specific event happens, such as a timesheet being approved. The receiving system can then act on it right away, without polling.

## How webhooks work

You register a URL and choose the events you care about. When such an event occurs, the sending system posts a small JSON message to that URL describing what happened. If the receiver is down, a good sender retries later.

Because anyone could post to a public URL, webhooks are signed. The sender computes an HMAC signature over the message with a shared secret; the receiver recomputes it and only trusts messages where the signatures match.

## Webhooks in TimeTracking

TimeTracking sends webhooks when hours change status, signed with HMAC and retried on failure. You can use them to update a CRM, start an invoice run or post a message in a chat channel. The REST API, with an OpenAPI spec, covers the other direction: reading and writing data on demand.

- [API and integrations](https://timetracking.tech/features/api-and-integrations)
- [MCP](https://timetracking.tech/glossary/mcp)
- [Audit trail](https://timetracking.tech/glossary/audit-trail)