What is a Webhook? - Explanation & Meaning

Definition

A webhook is an HTTP callback that automatically sends a message (HTTP POST request) to a specified URL when a specific event occurs. Webhooks enable real-time, event-driven communication between systems without the need for continuous polling.

Technical explanation

Webhooks follow a publisher-subscriber model: a source service (publisher) sends an HTTP POST request with a JSON payload to a receiver-specified endpoint (subscriber) when an event occurs. Examples include a payment provider sending a webhook on a successful payment, or GitHub triggering a webhook on a push to a repository. Security is crucial: webhooks must be verified via HMAC signatures (a hash of the payload with a shared secret) to prevent malicious actors from sending fake events. Retry mechanisms with exponential backoff ensure reliable delivery during temporary receiver failures. Idempotent handling prevents an event from being processed multiple times when the same webhook is resent. Webhook queues (via message brokers like RabbitMQ or Redis) decouple receipt from processing for better scalability. Monitoring webhook delivery with dashboards for success rates and failure ratios is essential. The difference with polling is fundamental: with polling, the receiver repeatedly asks for updates (wastes resources), with webhooks, the source proactively sends updates (efficient and real-time).

How MG Software applies this

MG Software implements webhooks as a standard integration mechanism in the applications we build. We use webhooks for payment notifications (Stripe, Mollie), CI/CD triggers (GitHub), CRM synchronization, and real-time data updates between systems. All webhook endpoints are secured with HMAC signature verification and equipped with retry logic and idempotent processing.

Practical examples

• An online store receiving a Stripe webhook on a successful payment, after which the order is automatically confirmed, an invoice generated, and a shipping label created.
• A CI/CD pipeline that is automatically triggered by a GitHub webhook on every push to the main branch, without the system needing to continuously poll the repository.
• A marketing automation receiving real-time notifications via HubSpot webhooks when a lead fills out a form, after which a personalized follow-up email is sent within seconds.

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