Webhook in practice
A webhook is a message that a program sends to a web address as soon as an event occurs: a payment received, a form submitted, a booking cancelled. Instead of checking every few minutes whether there is anything new, the other system is notified straight away and can react.
For a business it means instant automations. A client pays online and at that very moment the management software marks the order as paid, the confirmation email goes out and the warehouse gets the order to pack. Nobody has to update anything by hand.
An everyday example: a client books an appointment on your site. The booking system sends a webhook, which creates the event in your calendar and schedules the automatic reminders to go out before the visit. If the client cancels, a second webhook frees up the slot and cancels the reminders.
Two practical points. First, the address that receives the webhook must be protected, by checking that the message really comes from the expected service and not from just anyone. Second, webhooks sometimes arrive twice or late, so the receiving side must handle that without, for example, recording the same payment twice. Not every software offers them: when they're missing, you fall back on a periodic check with a cron job.
