"Webhook vs API" is a slightly odd matchup, because a webhook is delivered over an API. Both move data between systems over HTTP. The real difference is direction: with an API you ask for data when you want it; with a webhook the other system sends you data the moment something happens. One is pull, the other is push. Get that distinction and the rest follows.
What is an API?#
An API (in the everyday sense, a request-response HTTP or REST API) is something you call. Your code sends a request, the server does the work and sends a response. You decide when it happens. Want the latest order status? You make a request and get the current state back.
This is the pull model. The data sits on the server until you go and fetch it. If you want to know when something changes, you have to keep asking, which is called polling: hit the endpoint every few seconds or minutes and compare. APIs are ideal for on-demand reads and actions, where you want an answer right now and you are the one who initiates.
What is a webhook?#
A webhook flips the direction. Instead of you calling the provider, the provider calls you. You register a URL with them, and when an event happens (a payment succeeds, a build finishes, an issue is filed) they send an HTTP POST to your URL with the details. You do nothing until the event fires.
This is the push model, sometimes called a "reverse API." The provider initiates, and you just need an endpoint ready to receive. A webhook delivers the news as it happens, so you skip the constant asking.
Is a webhook a REST API?#
Not quite, even though a webhook travels over HTTP the same way a REST call does. A REST API exposes resources you request on your own schedule; there is always something to GET or a state to query. A webhook has no resource to fetch and no schedule; it is a one-way notification the provider sends unprompted, usually as a single POST with no follow-up request expected. So "webhook vs REST API" is really push notification versus pull-based resource interface, not two versions of the same thing. If you're designing the resource side, see API design principles.
Webhook vs API: the core difference#
| Dimension | API (request-response) | Webhook |
|---|---|---|
| Direction | You request, server responds (pull) | Server calls you on an event (push) |
| Who initiates | Your code (the client) | The provider (the server) |
| When data moves | When you ask for it | When something happens |
| Best for | On-demand reads and actions | Real-time event notifications |
| To get updates | Poll on a schedule | Received automatically |
| You must have | Access to the provider's API | A public URL to receive the call |
A short way to remember it: an API is you calling out, a webhook is them calling in.
Polling vs webhooks: why push wins for events#
Say you want to know when a payment clears. With an API you poll: check every 30 seconds. Most of those calls return "nothing changed," so you burn requests and rate limits to find out something happened up to 30 seconds late. Make the interval shorter and the waste grows; make it longer and you react slower.
A webhook removes the tradeoff. The provider POSTs to your endpoint the instant the payment clears: no wasted calls, no polling delay. For anything event-driven, a webhook is cheaper and faster than polling an API. The catch is that you now have to run and secure an endpoint that is always ready to receive.
When to use each#
Reach for an API when you control the timing: loading data on a page, running a report, creating or updating a record, or doing a one-off lookup. If the question is "what is the state right now," you pull.
Reach for a webhook when you care about events as they occur: payment and subscription changes, CI/CD pipeline results, form submissions, deploy notifications, or third-party status updates. If the question is "tell me the moment this happens," you let it push.
In practice most integrations use both. A webhook tells you something happened; you then call the API to fetch the full, current details, because webhook payloads can be minimal or arrive out of order.
Webhook tradeoffs to know about#
Webhooks move work onto you. Your endpoint must be publicly reachable, fast to respond, and able to handle bursts. Delivery is not guaranteed: if your server is down when the event fires, you can miss it, so good providers retry with backoff and you should make your handler idempotent in case a retry double-delivers. Security matters too, since anyone who learns the URL can POST to it, so you verify a signature on each request. And because the provider chooses when to send, debugging means inspecting what actually arrived, not re-running it on demand. None of these are dealbreakers; they are just the cost of the push model.
How this connects to monitoring#
Both sides show up in monitoring. You monitor an API by polling it on a schedule, which is exactly what an uptime or synthetic check does: call the endpoint, verify the status code and response, and time it. You receive monitoring alerts through a webhook, where the tool POSTs to Slack, PagerDuty, or your own service the moment a check fails.
ObserveOne does both: it runs scheduled checks against your API and web endpoints from multiple regions, asserts on status, body, and response time, and pushes alerts to your channels by webhook when something breaks. If you also expose webhooks of your own, it is worth pointing a check at the receiving endpoint too, since a silently broken webhook handler is a common blind spot.
The short version#
An API is pull: you request data when you want it. A webhook is push: the provider sends data when an event happens. Use an API for on-demand reads and actions; use a webhook for real-time notifications instead of polling. Most real systems use both, with a webhook signaling the event and an API call fetching the details. If you are wiring these together, the API monitoring guide and how to choose an API testing tool are good next reads.