What Is a Webhook? Automated HTTP Callbacks Explained

A webhook is an automated HTTP request that one application sends to another when a specific event occurs — essentially a reverse API call where the source app pushes notification to a URL you provide, instead of your app constantly polling "anything new yet?" Webhooks power payment confirmations, form submissions to Slack, CI/CD deploy triggers, and CRM updates across modern SaaS integrations.

What It Is

Traditional REST API polling:

`

Your server every 5 min: "Any new orders?" → Shop API: "No."

Your server: "Any new orders?" → Shop API: "No."

Event happens.

Your server: "Any new orders?" → Shop API: "Yes, order #99."

`

Webhook model:

`

You register URL: https://yourapp.com/hooks/new-order

Order placed → Shop instantly POSTs JSON to your URL with order details

Your server processes immediately

`

The webhook payload is usually JSON describing the event — type, timestamp, object IDs, relevant fields. Your endpoint validates authenticity (shared secret signature, HMAC), returns HTTP 200 quickly, and queues heavy work asynchronously if needed.

Named "web hook" historically — hooking into web events. Providers document supported event types — payment_intent.succeeded, push, issue.created.

Why It Matters

Real-time automation — send welcome email within seconds of signup, not after next cron poll.

Efficiency — eliminates wasteful polling traffic and API rate limit burn when nothing changed.

Decoupling systems — Stripe, GitHub, Shopify, Twilio notify your microservice without custom bilateral protocols for each pair.

Reliability expectations — providers retry failed deliveries with exponential backoff if your endpoint returns 5xx or times out — design idempotent handlers (same event twice should not double-charge).

Developer experience — no-code tools (Zapier, Make, n8n) expose "Webhook trigger" blocks — same concept, less code.

How It Works

Setup steps:

1. Implement HTTPS endpoint on your server — /webhooks/stripe

2. Register URL in provider dashboard — select event types

3. Provider sends test ping — verify signature validation works

4. On live event, provider POSTs payload with headers like Stripe-Signature

5. Your code verifies signature, parses JSON, updates database, responds 200 OK within timeout (often 5–30 seconds max)

Security essentials

• HTTPS only — no plain HTTP endpoints in production
• Verify signatures — never trust raw POST body without HMAC check using provider secret
• Reject replay — timestamp tolerance windows prevent old event replay attacks
• Secrets in env vars — not committed to Git

Idempotency

Networks duplicate deliveries — store processed event IDs and skip duplicates safely.

Async processing

Acknowledge fast; queue email sends or PDF generation — providers penalize slow endpoints with retries flooding your server.

Common Examples

| Provider | Example webhook event |

|----------|----------------------|

| Stripe | checkout.session.completed |

| GitHub | pull_request.opened |

| Shopify | orders/create |

| Twilio | Incoming SMS status callback |

| Typeform | Form submission |

| Jenkins / GitHub Actions | Push triggers deploy script |

Discord and Slack incoming webhooks are simpler — single URL posts formatted messages without full event subscription model.

Common Misconceptions

"Webhook and API are the same"

APIs are request-response you initiate. Webhooks are events the provider initiates toward you. Most integrations use both.

"Webhooks always secure out of the box"

Security depends on your verification code and secret hygiene. Public URLs without signature checks accept forged spam events.

"Returning 200 means work finished"

Best practice: 200 after durable enqueue — not after all side effects complete — lest retries duplicate work on timeout.

"Webhooks replace message queues entirely"

High-volume systems often place webhook receiver in front of Kafka/RabbitMQ/SQS — webhook is ingress, queue is processing backbone.

"Local development impossible without public URL"

Tools like ngrok, Cloudflare Tunnel, and webhook.site expose dev machines temporarily for testing provider callbacks.

"Webhooks send data only once"

Providers retry on failure — sometimes multiple times over hours. Your handler must tolerate duplicate deliveries of the same event ID without creating duplicate orders, emails, or database rows.

Webhooks vs. Polling — A Practical Comparison

Polling every minute for new orders means 1,440 API calls per day even when nothing happened. A webhook fires once per event — cheaper, faster, and easier on rate limits. The tradeoff is operational: you must run a reliable HTTPS endpoint that stays online, whereas polling only requires outbound requests from your side.

The Takeaway

A webhook is an event-driven HTTP callback — one system automatically POSTs data to your URL when something happens, enabling real-time integrations without constant polling. Implement HTTPS, signature verification, idempotency, and fast acknowledgment for production-ready webhook endpoints.

Practical takeaways

If you only remember a few points from this explainer, make them these: start with the plain-English definition, then match it to a real situation you already face (a device, a website, a work task, or a household decision). Next, notice the trade-offs — speed versus control, convenience versus privacy, simplicity versus flexibility — because most technology and money terms hide a trade-off rather than a pure upgrade. Finally, verify details against an official source before you change settings, sign documents, or spend money. Definitions on the internet go stale; product screens and regulations change.

When to dig deeper

You do not need a textbook for every search query. Dig deeper when money, identity, legal rights, or account security are involved; when a tutorial asks you to disable protections; or when two reputable sources disagree. In those cases, prefer primary documentation (vendor help pages, standards bodies, government consumer pages) over viral summaries. A clear mental model plus one trusted checklist usually beats collecting ten half-read explainers.

*This article is for general informational purposes only and does not constitute professional software architecture advice.*