When your payment processor confirms a card, or your calendar fills a slot, that system fires a small message at a URL you designate, carrying the details of what just happened. Your platform catches it and reacts in the same second: send the confirmation, update the record, notify the crew. Every automation that feels instant is usually a webhook underneath.
Because it defines what your tools can and cannot do together. When software advertises integrations, the real question is which events it announces and which it can hear. A booking tool with rich webhooks can drive your whole follow-up machine; one without them traps your data behind manual exports. It is a purchasing criterion disguised as a technical term.
Production webhook handling verifies the sender, so forged events cannot fake a payment, and survives the messy reality that events sometimes arrive twice or late. Handlers must be idempotent, a duplicate delivery must not send two receipts or double-book a crew. This unglamorous rigor is a lot of what separates automation that runs for years from automation that works in the demo.
An API is you asking a system for information when you want it; a webhook is the system telling you the moment something changes. Real integrations usually use both directions.
Automation platforms let non-developers catch simple ones. Anything involving money, scheduling, or customer records deserves engineering, because the failure modes are silent and expensive.
Good senders retry; good receivers reconcile on a schedule to catch anything missed. Systems built without that assumption eventually disagree about reality.
Everything in this glossary, we build and operate for real businesses. Thirty minutes maps it to yours.