API vs Webhook: What Is the Difference?

An API call is a request your system initiates — 'has this order shipped yet?' — sent whenever you choose to send it, with the other system replying immediately with whatever the current answer is. Nothing happens until you ask.

A webhook flips that around. Instead of your system repeatedly asking, the other system is configured to send you a message the instant something relevant happens on its side — 'this order just shipped' — without you having to ask at all. You register a URL with the other system in advance, and it calls that URL whenever the event you subscribed to occurs.

Repeatedly calling an API to check for a change — known as polling — gives you full control over timing but trades that off against latency and load: if you check every ten minutes, you find out about a change up to ten minutes late, and checking more often means more requests, which many providers rate-limit or charge for.

A webhook typically delivers near-instant notification with far less wasted traffic, since nothing is sent until there's actually something to report. The tradeoff is control and reliability on the receiving end — your system has to be reachable and ready to accept the webhook at any moment, and if your server is briefly down when it arrives, you depend entirely on the sender retrying, which not every provider does reliably or for long.

Consider an online electronics store shipping through a courier partner — a business that, like most, ends up using both patterns in the same order journey. When the order is first created, the store calls the courier's API directly to book the pickup and get a tracking number — a request it controls and initiates.

After that, rather than repeatedly asking the courier 'has this been delivered yet?' all day, the store registers a webhook so the courier's system notifies it the moment the parcel's status changes — out for delivery, delivered, or a failed attempt — without the store's system needing to keep asking.

Both patterns need to be secured, but differently. An outgoing API call is authenticated with a key or token you send along with your request. An incoming webhook needs the reverse check — proving the request landing on your server genuinely came from the courier and not from someone who guessed your webhook URL — usually done by verifying a signature the sender includes, the same principle covered for payment gateway webhooks elsewhere on this site.

Both also need duplicate handling. An API call you retry after a timeout might end up executing twice if the first attempt actually succeeded but the response was lost; a webhook provider might deliver the same event more than once by design, to be safe. Either way, the receiving system should check a unique reference — an order ID, an event ID — before acting on the same thing twice.

As a rough rule: use an API call when you need an answer right now, on demand, or when you're initiating an action (booking a pickup, charging a payment). Use a webhook when you need to know about something the other system does in its own time, and being told promptly matters more than controlling exactly when you ask.

Many mature integrations end up using both for the same relationship, exactly as in the courier example — API calls for the actions you initiate, webhooks for the events you need to react to. Choosing only one pattern for every situation usually means either wasting resources on unnecessary polling, or missing the ability to trigger actions on your own schedule.