A webhook is a reverse HTTP-based API
An HTTP-based API allows a client to request information with GET requests to specific endpoints. For example, a client might be interested in the /is-complete endpoint, and could issue a GET request to get the response of TRUE or FALSE.
However, in this scenario, it’s likely that the client wants to know when the /is-complete endpoint turns from FALSE to TRUE, and using an API is forced to continuously poll the server until the response changes.
Instead, wouldn’t it be better if the server just let the client know when the /is-complete endpoint turns from FALSE to TRUE? That’s what webhooks do by being a reverse API – instead of the client sending a GET request to the server, the server sends a POST request to the client.
Setting up a webhook
Since the server needs to send a POST request to the client, the client needs to have an HTTP endpoint that’s prepared to handle the request.
The webhook package is a very nice and lightweight way to implement this.
Then, you just need the server to send a POST request whenever required (github has built in functionality for this).
Testing a webhook using cURL
The curl command in linux can be used to send HTTP requests, and thus test the webhook:
curl -X POST -H "Content-Type: application/json" -d "{ "your_data": "your_value" }" <your_webhook_url>