APIs and webhooks are two ways applications share data. An API lets your application pull data from a server on demand. A webhook pushes data to your application automatically when a specific event occurs, with no request needed.

TL;DR

• Use APIs for on-demand data access, complex queries, and actions (CRUD).
• Use webhooks for event-driven notifications without polling.
• Most systems combine both: webhooks for awareness, APIs for follow-up details and actions.
• APIs offer control but can waste calls via polling; webhooks are efficient but need retries and validation.
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What Is an API?

An Application Programming Interface (API) is a set of protocols that lets software applications communicate through a request-response model. The client sends a request using standard HTTP methods:

• GET to retrieve data
• POST to create records
• PUT to update them
• DELETE to remove them

The server processes the request and returns a response.

The client controls when and what data is fetched. You can structure complex queries with parameters, filters, and pagination to retrieve exactly the data you need. Common architectural patterns include REST (Representational State Transfer, the most widely used, built on HTTP), GraphQL (a query language that lets clients specify exact data requirements), and gRPC (a high-performance protocol using HTTP/2 and binary serialization for service-to-service communication).

APIs authenticate requests through API auth methods. Communication is synchronous by default: your application sends a request and waits for the response before proceeding.

For instance, when you search for a song on Spotify, the client sends an HTTP GET request to Spotify's REST API with your search query as a parameter. The API returns matching results as a JSON (JavaScript Object Notation) response. You initiated the request. The server responded. That's the pull model.

What Is a Webhook?

A webhook is an automated HTTP callback triggered by a specific event in a source system. Instead of your application calling the server, the server calls your application. This is why webhooks are sometimes called "reverse APIs."

The source sends data only when something happens: a payment is processed, a commit is pushed, a support ticket is created. It delivers an HTTP POST request to a URL you've pre-registered (your webhook endpoint) with a payload, typically JSON. Your endpoint acknowledges receipt with a 200 OK status code, then processes the payload asynchronously.

Webhooks are limited to one-way event notification. They cannot retrieve data, perform queries, or execute CRUD (Create, Read, Update, Delete) operations. To access detailed information after a notification, you call an API. This is why most production systems combine both: webhooks notify you something happened, APIs let you fetch complete data or take action.

When a customer completes a payment in Stripe, for instance, Stripe sends an HTTP POST to your webhook endpoint with the payment details: amount, currency, customer ID, payment method. You didn't ask for it, Stripe pushed it the moment the event occurred.

What Is the Difference Between a Webhook and an API?

The distinction comes down to communication direction, efficiency, and control.

Pull vs. Push

The fundamental difference is who initiates communication. APIs pull data on your schedule. Webhooks push data on the source's schedule, triggered by events you've subscribed to. APIs give you control over timing and queries. Webhooks give you immediacy without the overhead of asking.

The Polling Problem

If you need near-instant updates via an API that doesn't support push or streaming, the common approach is polling: sending repeated requests at fixed intervals to check for changes. Most of these requests return unchanged data, which wastes network traffic and consumes API rate limits.

Polling 100 endpoints every 30 seconds generates 12,000 requests per hour. GitHub rate limits cap authenticated requests at 5,000 per hour. Polling just 42 endpoints every 30 seconds would exhaust your entire budget with zero capacity left for actual operations.

Webhooks eliminate this waste by firing only when events occur. During idle periods, they consume zero bandwidth and zero server processing.

When Should You Use an API?

Use APIs when your application needs to fetch data on demand, whether that's user profiles, product catalogs, search results, or analytics reports. APIs support full CRUD operations, so any workflow that creates, updates, or deletes records needs one.

APIs also make sense for complex queries like filtering by price range, paginating through thousands of records, or aggregating across dimensions. If you need the current state at a specific moment (checking inventory before placing an order, verifying a balance before a transfer), an on-demand call gives you the freshest snapshot.

Two-way communication is another clear signal. CRM (Customer Relationship Management) synchronization, mobile offline sync, and collaborative editing all require APIs because both sides need to read and write data.

When Should You Use a Webhook?

Use webhooks when you need immediate notifications about unpredictable events. Completed payments, shipped orders, triggered builds, and new registrations all occur on their own schedule. A form submission once a day doesn't justify polling every five seconds.

Webhooks also reduce API call costs, which matters when you're paying per call or operating under strict rate limits. They excel at triggering downstream workflows: a new support ticket arrives via webhook, notifies a Slack channel, updates the CRM, and assigns the ticket to an agent.

Webhook vs. Api: What Are the Tradeoffs?

Both patterns introduce complexity that scales with the number of integrations you maintain.

API Tradeoffs

Each API has its own authentication pattern (API keys, OAuth 2.0, JSON Web Tokens), pagination approach (cursor-based, offset-based, keyset), and error handling conventions. Integrating with multiple APIs means writing and maintaining connection code for each one. 

Different providers implement different rate limiting algorithms (token bucket, sliding window, fixed window), so retry logic must adapt per source. When a provider updates their schema (renaming fields, changing data types, restructuring nested objects), your integration breaks until you update your transformation logic.

Webhook Tradeoffs

If your endpoint is down when an event fires, you miss it. Most providers implement retry logic with exponential backoff, but retry windows are finite. Events that exhaust all retries land in dead-letter queues for manual processing.

You also expose a public endpoint that accepts incoming HTTP requests. This creates a security surface different from outbound API calls. Validate incoming requests using HMAC verification (Hash-based Message Authentication Code): the source signs the payload with a shared secret, and you verify it using a timing-safe comparison. Every provider implements this differently, so you need provider-specific validation logic. Use HTTPS for transport encryption and whitelist source IPs where available.

Debugging is harder because delivery is decoupled from the triggering event. You need visibility into delivery status, failures, and retry history. If the payload lacks the data you need, you must follow up with an API call.

How Do Webhooks and APIs Relate to AI Agent Data Access?

AI agents need data from enterprise tools: CRMs, ticketing systems, communication platforms, and document stores. An agent reasoning over customer support tickets might poll a ticketing API for current state and receive webhook notifications when new tickets arrive. In practice, most agent data access requires handling both patterns across dozens of sources, each with different authentication flows, rate limits, schemas, and event formats.

That volume turns into an infrastructure problem. Building connections to each tool requires custom OAuth flows, rate limit handling, schema normalization, and retry logic, and the work multiplies with every new source. Whether data arrives through polling or push, it must be normalized into consistent formats, enriched with metadata, and delivered with proper permissions. This context engineering work often takes months before any AI-specific functionality can be implemented. Data preparation, not model capability, creates the bottleneck.

How Does Purpose-Built Infrastructure Handle Both Patterns?

For AI agents, the challenge is managing both patterns across dozens of enterprise sources, each with different authentication flows, rate limits, schemas, and event formats. 

Airbyte's Agent Engine provides the data infrastructure layer: API access across 600+ sources, Change Data Capture (CDC replication) for sub-minute data freshness, schema normalization, and cross-system entity resolution through the Context Store.

Access controls ensure agents only reach authorized data, and the embeddable widget lets end users connect their own sources without engineering work. PyAirbyte adds a Python-native interface that integrates into agent workflows and orchestration code.

Connect with an Airbyte expert to see how Airbyte powers AI agents with governed access to enterprise data.

Frequently Asked Questions

Do webhooks and APIs use different communication models?

They are complementary patterns that both use HTTP but implement different communication models. Webhooks are built on top of API infrastructure (they send HTTP POST requests to endpoints), but they are limited to one-way event notifications. APIs support bidirectional request-response communication with full query control.

Can you use webhooks and APIs together?

Yes, and most production systems do. A common pattern is to receive event notifications via webhook (new order, ticket update), then call an API to fetch details or take action. CI/CD pipelines follow the same approach: a webhook fires on code push, then API calls fetch commit details, trigger builds, and update deployment status.

What is the difference between webhooks and WebSockets?

Webhooks are one-way HTTP callbacks: the source pushes data, then the connection closes. WebSockets provide persistent, full-duplex communication where both sides send messages simultaneously over an open connection. Use webhooks for discrete server-to-server notifications like payment confirmations or deployment triggers. Use WebSockets for continuous bidirectional streams like collaborative editing, live trading feeds, chat, or multiplayer games.

How do you secure a webhook endpoint?

Validate incoming requests using HMAC verification: the source signs the payload with a shared secret, and you verify it with a timing-safe comparison. Use HTTPS for transport encryption and whitelist source IPs where available. Respond with 200 OK quickly before processing asynchronously to avoid timeouts, and implement dead-letter queues for events that fail validation or processing.

Can webhooks replace APIs entirely?

No. Webhooks only push event notifications in one direction. They cannot retrieve historical data, run queries, or perform create, update, or delete operations. Any workflow that requires on-demand data access, two-way communication, or complex filtering still needs an API. Webhooks reduce the need to poll for changes, but they depend on APIs for follow-up actions and complete data retrieval.

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