Webhook.

An automatic Trigger that fires the moment something happens. A message arrives, a payment lands, and the webhook instantly pings another app to say "this just happened, go." One app tapping another on the shoulder the instant an event occurs.

The contrast that makes it click: the other way to catch an event is a Cron loop, where your agent keeps waking up on a schedule to check whether anything changed. A webhook flips that. Nothing checks on a timer. The event itself does the triggering.

Remy framed it against Claude Code: a tool "configured with something like a webhook" gets triggered automatically the moment you send it a message, "whereas with Claude Code we have to set a loop to trigger it." Webhooks are instant and event-driven. Loops are scheduled and always a little behind.