Webhook

A webhook is a way for one service to notify yours the instant something happens, by sending a message to a URL you control. Instead of your product repeatedly asking "has the payment gone through yet?", the payment provider simply pings your webhook the moment it does. It is event-driven plumbing: the source pushes to you rather than you polling it. For a lean founder, webhooks are how you make integrations feel instant and keep systems in sync without wasteful checking, a new subscription updates your database the second it happens, a failed charge triggers an email automatically. The catch is reliability: webhooks can arrive twice, out of order, or get retried, so your handler must be written to cope, typically by checking whether it has already processed that event before acting. They are also a security surface, since anyone could hit that URL, so you verify each incoming message genuinely came from the provider before trusting it.