# What is a webhook, and what happens when your system misses one?

A webhook is one system calling a URL of yours the moment something happens, instead of you asking repeatedly whether it has. It is how a payment, a form submission or an alert reaches your system within a second. The catch is that delivery is the sender's problem, so a missed call is usually silent.

Also called: callback URL, HTTP callback
Checked: 2026-09-27

In one line

They call you when it happens, instead of you asking every minute.

## Why it matters to you

Two failure modes cause most webhook incidents, and both are straightforward to handle if you know about them in advance.

The first is duplicates. Many senders retry when your endpoint is slow or returns the wrong status, so the same event can arrive twice. An endpoint that charges a card or sends a mail without checking whether it has already seen that event id will eventually do it twice.

The second is loss. If your endpoint is down when the sender calls, some senders retry for a while and some give up immediately, and either way nothing appears in your logs because the request never arrived. A system that only learns about events through webhooks needs a periodic reconciliation against the source of truth, or it will quietly drift.

## Where it turns up in something we run

- A Cloudflare Worker takes Sentry alert webhooks and posts them into a Telegram supergroup with full-context attachments, for every OCTYN project (recorded 2026-07-06, [Error relay](https://octyn.co/casestudies/sentry-telegram-relay))
- Deploys on octyn.co run through a push, a webhook, a build and a rolling restart, and the same pattern runs every other OCTYN site (recorded 2026-09-14, [octyn.co](https://octyn.co/casestudies/octyn-site))

## Next to this

- [Orchestration](https://octyn.co/glossary/orchestration)
- [Observability](https://octyn.co/glossary/observability)

## Argued out at length

- [A glued workflow versus a built system at 10,000 runs a month](https://octyn.co/compare/glued-workflow-vs-built-system)

## Related

- [A glued workflow versus a built system at 10,000 runs a month](https://octyn.co/compare/glued-workflow-vs-built-system)
- [Orchestration](https://octyn.co/glossary/orchestration)
- [The Consult](https://octyn.co/consult)

Canonical: https://octyn.co/glossary/webhook