A webhook is an automatic HTTP request that one app sends to a URL you choose when an event happens, such as a new sign-up or a form message.
Without webhooks, one app has to ask another again and again whether anything is new. With a webhook, the first app sends the news to your URL as soon as it happens. That is why webhooks are sometimes called reverse APIs.
A webhook request usually carries JSON that describes the event, plus a signature header. The receiver checks the signature with a shared secret, so it knows the request is genuine.
Automation tools such as Zapier, Make, and n8n give you a webhook URL, so you can connect apps without writing a server.
Example
Each time someone sends a contact form, a webhook posts the message to a Zapier URL, and Zapier adds a row to a Google Sheet.
In pageo
pageo Pro sends a signed webhook for each new subscriber and each form message, with retries and a delivery log in settings.
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