Interfaces and protocols
Webhook
In short and in plain language
A webhook turns the flow around. No program has to keep asking. The program with the change reports it at once. The message goes to a set address.
That saves requests. News can get there faster.
But the other side must be reachable. It must also guard against calls that are sent twice or faked.
Definition
A webhook reverses the direction: instead of polling regularly, the sending system reports a change immediately via an HTTP call to a registered address. That saves requests and shortens reaction time, but it requires a reachable endpoint and protection against duplicate or forged calls.