Webhooks vs APIs: What's the Difference?

Most products today integrate with payment platforms, identity providers, messaging services, and analytics tools. Two communication models power the majority of these integrations: APIs and webhooks.

Both use HTTP, but they solve different problems. An API lets one application request data or trigger actions on another system. A webhook automatically sends data when a specific event occurs. Knowing when to use each — and how to combine them — is a core skill for building reliable integrations.

Understanding APIs

An API (Application Programming Interface) is a defined interface that allows one application to interact with another. APIs expose specific operations that external systems can call to retrieve data or trigger actions.

Most web APIs operate over HTTP and follow a request–response model: a client sends a request, the server processes it, and the server returns a response. APIs act as controlled gateways — instead of exposing internal databases or services directly, they surface only what external callers need.

A typical SaaS application might expose APIs to:

• Retrieve user profile data
• Create or update resources
• Fetch analytics
• Manage account settings
• Trigger operational workflows

Because the client initiates every request, APIs are pull-based: your system fetches data whenever it needs it.

How APIs Work

API Request–Response Flow

1. Client sends request. A mobile app, frontend, or backend service sends an HTTP request to an API endpoint.
2. Authentication is validated. The server verifies the caller using API keys, OAuth tokens, or session credentials.
3. Server processes the request. The server performs the requested operation — querying a database, executing business logic, or calling other services.
4. Server returns response. The API responds with a status code and any requested data.
5. Client handles the result. The client interprets the response and continues its workflow.

A dashboard that calls an analytics API on every page load is a classic example: the client pulls fresh data on demand, exactly when it needs it.

What Are Webhooks?

Webhooks work in the opposite direction. Instead of waiting for a client to ask, the system automatically sends data to a configured endpoint when something happens.

A webhook is an automated HTTP POST request triggered by an event. The sending system packages event data into a JSON payload and delivers it to a URL you register in advance.

Common webhook events include:

• A new user registration
• A successful payment
• A completed deployment
• A subscription cancellation
• A user login or authentication event

Because the server initiates the communication, webhooks are push-based: data arrives automatically when events occur, without your system needing to ask.

How Webhooks Work

Webhook Event Flow

1. Register a webhook endpoint. Your application provides a URL where it wants to receive event notifications.
2. Event occurs in the source system. A payment succeeds, a user signs up, an authentication event fires.
3. Source system builds a payload. The platform creates a structured JSON object describing the event.
4. HTTP POST is sent. The system delivers the payload to your registered endpoint.
5. Your server processes the event. You validate the request and trigger whatever action makes sense — update a record, send an email, log the activity.

A typical webhook payload looks like this:

{
  "event": "user.login",
  "timestamp": "2026-03-13T17:00:00Z",
  "resource_id": "usr_abc123",
  "metadata": {
    "ip_address": "203.0.113.42",
    "user_agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7)..."
  }
}

Because webhooks only fire when events occur, they are far more efficient than polling for real-time notifications.

Webhooks vs APIs: Key Differences

The core distinction is who initiates communication. With APIs, your system asks for data. With webhooks, the other system tells you when something happens.

API Polling vs Webhooks

Polling means repeatedly calling an API to check whether something has changed — for example, checking every few seconds whether a payment has completed.

Polling Workflow

1. Client requests current status
2. Server returns current status
3. Client waits a few seconds
4. Client requests again
5. Repeat until status changes

This works, but it's wasteful. If thousands of clients poll the same endpoint every few seconds, you're generating enormous traffic for data that usually hasn't changed.

Webhook Workflow

1. Event occurs in source system
2. Server sends one webhook notification
3. Your server processes the update

Webhooks eliminate unnecessary requests entirely and reduce latency — your system reacts the moment an event fires, not on the next poll interval.

Real-World Examples

Most modern platforms use APIs and webhooks together.

Payment Platforms

• Your app creates a payment session via API
• The customer completes payment on the provider's page
• The payment provider sends a webhook confirming success
• Your app updates the order status and triggers fulfillment

Stripe, for example, uses both: the API to create charges, and webhooks to deliver payment_intent.succeeded or charge.failed events asynchronously.

CI/CD Pipelines

• A push to the main branch triggers a webhook from GitHub
• The CI system starts the build pipeline
• Build status and logs are retrieved via the CI API

Authentication Platforms

Identity platforms use webhooks to deliver events your app can act on in real time:

• New user registrations
• Login activity
• Password reset requests
• Account deletions

These events power analytics tracking, security monitoring, onboarding automation, and audit logging — without your app having to poll for identity state changes.

Webhook Security

Anyone on the internet can POST to your webhook endpoint. Without proper validation, attackers can send spoofed events. Implement these protections:

Signature Verification

Most webhook providers include a cryptographic signature in the request headers (e.g. X-Signature-256). Compute the expected HMAC using your shared secret and reject requests where the signatures don't match. This is the most important protection — do not skip it.

HTTPS Only

Always use HTTPS for webhook endpoints. Without it, payloads travel in plaintext and can be intercepted or modified in transit.

Timestamp Validation

Webhooks often include a timestamp in the payload or headers. Reject events with timestamps older than a few minutes — this prevents replay attacks where an attacker resends a captured valid request.

IP Allowlisting

Some providers publish the IP ranges they use for webhook delivery. Restricting inbound requests to those addresses adds a second layer of defense.

Idempotent Processing

Webhook providers retry failed deliveries — your endpoint may receive the same event more than once. Design your handler to be idempotent: processing the same event twice should produce the same result as processing it once. Use the event ID to deduplicate.

Webhook Reliability

If your webhook endpoint is down when an event fires, the delivery fails. Most platforms handle this with:

• Automatic retries with exponential backoff
• Delivery logs showing success/failure per event
• Dead-letter queues for events that exhaust retries

Keep your endpoint fast. Return a 2xx status code immediately, then process the event asynchronously using a background job or message queue. If your handler does expensive work synchronously, it will time out and trigger retries.

API Design Patterns

REST APIs

REST is the most common API pattern. Resources map to predictable URLs, and HTTP methods define the operation:

GET    /users           # List users
POST   /orders          # Create an order
PUT    /accounts/{id}   # Update an account
DELETE /sessions/{id}   # Delete a session

GraphQL

GraphQL exposes a single endpoint that accepts structured queries. Clients request exactly the fields they need, which eliminates over-fetching and reduces the number of round trips for complex data requirements.

Rate Limiting

APIs typically enforce rate limits to prevent abuse and protect infrastructure. Design clients to respect 429 Too Many Requests responses and implement retry logic with backoff.

Webhook Implementation Patterns

Event Subscriptions

Rather than receiving every event a platform emits, subscribe only to the ones your integration needs:

Selective subscriptions reduce noise and make your handlers easier to reason about.

Structured Payloads

A good webhook payload always includes:

• Event type
• Timestamp
• Resource identifier
• Relevant metadata

Consistent structure across all events means you can write generic validation and routing logic rather than handling each event type differently.

Delivery Logs and Versioning

Use provider delivery logs to diagnose failed events during integration and debugging. When a platform evolves its payload format, versioning (e.g. X-Webhook-Version: 2) allows you to migrate consumers without breaking existing integrations.

Combining APIs and Webhooks

In practice, most integrations use both. A typical pattern:

1. Your app calls the API to create or update a resource
2. The platform performs the action
3. The platform fires a webhook when a related event occurs
4. Your app handles the event and updates its own state

Example with an authentication platform:

• API call creates a new user account
• User completes login
• Authentication event triggers a webhook to your app
• Your app logs the activity to your security monitoring system

When to Use APIs vs Webhooks

Use APIs when

• You need to retrieve or modify data on demand
• Your client controls the timing of requests
• You need to query with filters or perform complex operations
• You're triggering actions programmatically

Use Webhooks when

• You need to react to events in real time
• Polling the API would generate unnecessary load
• You need to trigger workflows based on external state changes
• You're building event-driven automation

Why Webhooks Matter for Authentication

Authentication systems are event-rich by nature. Every login, registration, password reset, MFA verification, and account deletion is an event your application may need to act on.

Without webhooks, your app would have to poll for identity state changes — an impractical approach for events that need immediate handling. Webhooks make it possible to:

• Detect and alert on suspicious login patterns in real time
• Trigger onboarding workflows the moment a user registers
• Revoke sessions or notify users when account changes occur
• Feed authentication events into audit logs or SIEMs

Authgear's webhook system delivers identity events — signups, logins, MFA completions, account deletions — to your endpoint as they happen, so your application can respond instantly rather than catching up on a polling interval.

Bottom Line

APIs and webhooks are complementary tools, not alternatives. APIs give your system control: fetch data and trigger actions when you need them. Webhooks give the other system a voice: it notifies you the moment something worth acting on happens.

For authentication integrations, webhooks are particularly valuable — identity events are time-sensitive, and polling for them doesn't scale. Building event-driven workflows around authentication activity produces more responsive, efficient systems.

To explore how Authgear handles webhook delivery, event types, and signature verification, see the Authgear events and hooks documentation. Or get started with Authgear to add authentication event webhooks to your application today.

FAQs

What is the difference between a webhook and an API?

An API requires your system to send a request to get data or trigger an action. A webhook sends data to your system automatically when an event occurs. APIs pull data on demand; webhooks push data in real time.

When should I use webhooks instead of polling an API?

Use webhooks when you need to react to events immediately and don't know when they'll occur. Polling works for scheduled data fetches but is wasteful for event-driven scenarios — you send many requests that return no new data.

Can APIs and webhooks be used together?

Yes — most integrations use both. APIs handle create/read/update/delete operations; webhooks deliver notifications when those operations produce events. A payment app might create a charge via API and receive a payment.succeeded webhook when the customer pays.

Are webhooks more efficient than API polling?

Yes. Webhooks send data exactly once when an event fires. Polling sends continuous requests regardless of whether anything has changed, which wastes bandwidth and increases server load on both sides.

How do I secure a webhook endpoint?

Validate the cryptographic signature included in every request (using your shared secret), enforce HTTPS, reject payloads with stale timestamps to prevent replay attacks, and design your handler to be idempotent so duplicate deliveries don't cause side effects.