Glossary · WebhookAlso called callback URL, HTTP callbackChecked 27 September 2026
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.
In one lineThey 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.
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