Types of APIs: REST, GraphQL, gRPC, WebSocket, Webhook and SOAP Explained

APIs are one of the most important parts of modern software applications. Whenever we use a mobile app, website, online shopping platform, food delivery app, banking application, or social media platform, APIs are often working in the background.

For beginners, the word API can sound complicated. However, the basic idea is very simple. An API allows two different software systems to communicate with each other and exchange information.

For example, imagine that you visit a restaurant. You sit at your table and look at the menu. You choose your food and give your order to the waiter. You do not go directly into the kitchen. The waiter takes your request to the kitchen and brings the food back to you.

An API works in a similar way. The application sends a request, the API carries that request to the server or another system, and the response is returned to the application.

There are different types of APIs, and each type is useful for a different situation. Some are best for normal web applications, some are designed for real-time communication, and others are useful for communication between internal services.

In this article, we will explain the most important types of APIs in very simple words and understand their real-world uses.

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What Is an API?

API stands for Application Programming Interface.

In simple words, an API is a communication interface that allows one application to communicate with another application or server.

For example, suppose you open a food delivery application and search for restaurants.

You may see:

• Restaurant names
• Food items
• Prices
• Customer ratings
• Delivery information
• Offers
• Your previous orders

All of this information usually comes from a server. Your mobile app needs a way to request this information from the server. The API acts as the communication layer between them.

The basic communication looks like this:

Client → API → Server → API → Client

The client can be a website, mobile application, desktop application, or another software system.

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Why Are APIs Important?

Modern applications are usually made from many different components. These components need to communicate with each other.

For example, an online food delivery application may have separate services for:

• User accounts
• Restaurants
• Orders
• Payments
• Delivery
• Notifications
• Offers

Without APIs, these systems would have difficulty communicating with each other.

APIs make it possible to exchange data and perform actions in a controlled way.

They also help developers build applications faster because one system can use information or services provided by another system.

Now let’s understand the major types of APIs.

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1. REST API

REST API is one of the most popular and widely used types of APIs for web applications.

REST stands for Representational State Transfer.

A REST API commonly works over HTTP or HTTPS and uses standard HTTP methods to communicate with a server.

For example, websites and mobile applications commonly use REST APIs to request data from a backend server.

A REST API usually treats data as resources.

For example:

• Users
• Products
• Orders
• Restaurants
• Payments

Each resource may have a URL or endpoint.

For example:

GET /users/123

This could mean that the application wants information about user 123.

Common HTTP Methods in REST

REST APIs commonly use these HTTP methods:

GET

GET is used to retrieve data.

For example:

GET /products

This may return a list of products.

POST

POST is generally used to create a new resource or submit information.

For example:

POST /orders

This could create a new order.

PUT

PUT is commonly used to replace or completely update a resource.

For example:

PUT /users/123

This may replace the information associated with user 123.

PATCH

PATCH is generally used for a partial update.

For example, if you only want to change a user’s phone number, PATCH can update only that field instead of replacing the entire user record.

DELETE

DELETE is used to remove a resource.

For example:

DELETE /orders/123

This could request deletion of order 123.

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REST API Example

Imagine that you open a food delivery app.

The application may make requests such as:

GET /restaurants

to retrieve restaurants.

Then it may request:

GET /restaurants/25/menu

to retrieve the menu of a particular restaurant.

It may send:

POST /orders

to create an order.

The server sends the response back, often in JSON format.

A simple JSON response might look like:

{
  "restaurant": "ABC Restaurant",
  "rating": 4.5,
  "deliveryTime": "30 min"
}

REST is popular because it is simple, flexible, easy to understand, and supported by almost every modern programming language and platform.

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2. GraphQL API

GraphQL is another important API technology.

One of the biggest advantages of GraphQL is that the client can ask for exactly the data it needs.

This can help avoid receiving unnecessary data.

Imagine a food delivery application needs:

• Customer name
• Last three orders
• Reward points
• Saved address
• Recommended restaurants

With multiple REST endpoints, the application may need to make several requests.

For example:

GET /customer

GET /orders

GET /rewards

GET /address

GET /recommendations

Depending on the API design, this could require several network requests.

GraphQL can allow the client to request many required fields through a single query.

A simplified GraphQL query might look like:

query {
  customer {
    name
    rewardPoints
    savedAddress
    recentOrders {
      id
      total
    }
  }
}

The server can then return the requested information.

Main Advantage of GraphQL

The major benefit is flexibility.

The client can request the fields that it needs instead of receiving a large amount of unnecessary information.

This can be especially useful for applications with complicated data requirements.

GraphQL is commonly used in applications where developers need flexible data fetching and where a single screen may require information from several related resources.

However, GraphQL is not automatically better than REST in every situation. The correct choice depends on the application’s requirements.

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3. gRPC API

Another important technology among the types of APIs is gRPC.

gRPC stands for Google Remote Procedure Call.

It was originally created at Google and is now an open-source project used for high-performance communication between services.

gRPC is especially useful in microservices architecture.

What Is a Microservice?

Imagine a large food delivery application.

Instead of building everything as one huge application, developers may create multiple services:

• Order Service
• Payment Service
• Restaurant Service
• Delivery Service
• Notification Service

These services need to communicate with each other.

For example:

Order Service → Payment Service

Payment Service → Order Service

Order Service → Restaurant Service

Delivery Service → Notification Service

This internal communication needs to be fast and efficient.

gRPC is often a strong choice for this type of communication.

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Why Is gRPC Fast?

Traditional REST APIs commonly exchange data using formats such as JSON.

JSON is easy for humans to read, but it can be larger and require parsing.

gRPC commonly uses Protocol Buffers (Protobuf), which provides a compact binary representation of structured data.

This can reduce message size and improve performance, especially for service-to-service communication.

gRPC also supports features such as strongly defined service contracts and different communication patterns, including streaming.

For these reasons, gRPC is frequently used in high-performance internal systems and microservice environments.

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4. WebSocket API

WebSocket is different from normal request-and-response communication.

It is mainly useful when an application needs real-time, two-way communication.

Think about applications such as:

• Live chat
• Live delivery tracking
• Online multiplayer games
• Live notifications
• Real-time dashboards
• Live sports updates

Suppose you ordered food and want to track your delivery driver.

With a traditional polling approach, the application might repeatedly ask:

“Where is my order?”

Then after some time:

“Where is my order now?”

Then again:

“Where is my order now?”

This repeated request can create unnecessary traffic.

WebSocket provides a persistent connection between the client and server.

Once the connection is established, both sides can send messages over the same connection.

For example:

Client ↔ Server

The connection remains open while it is needed.

The server can then send updated information when something changes.

This makes WebSocket useful for real-time applications.

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WebSocket and Real-Time Tracking

Imagine a delivery driver moving from one location to another.

Instead of repeatedly creating new requests, the server can send updated location information through the existing WebSocket connection.

The user may see the driver’s position changing on the map.

The same idea can be used in a live chat application.

When another person sends a message, the server can immediately send that message to the connected user.

This gives WebSocket a major advantage for real-time communication.

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5. Webhook

A webhook works using an event-based approach.

You can think of a webhook as an automatic notification sent from one system to another when something happens.

Imagine an online store using a payment service.

A customer buys a pair of shoes and completes payment through a payment provider.

The store does not necessarily need to keep asking:

“Was the payment successful?”

“Was the payment successful?”

“Was the payment successful?”

Instead, the store can provide a predefined URL called a webhook endpoint.

When the payment succeeds, the payment service sends an HTTP request to that endpoint.

For example:

Payment Successful → Payment Service → Webhook URL → Online Store

The store receives the event and can update the order status.

This approach reduces unnecessary polling.

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Webhook Security

Webhooks must be protected carefully.

An attacker should not be able to simply send a fake request and tell the application:

“Payment completed.”

For this reason, webhook systems often use security mechanisms such as:

• Signature verification
• Secret keys
• HMAC-based hashes
• Timestamps
• Replay protection
• HTTPS

The receiving server verifies the request before trusting the event.

For example, if the payment provider signs the webhook request, the receiving application can calculate or verify the signature.

If the signature is invalid, the request can be rejected.

Timestamps can also help prevent old requests from being reused as fake events.

Webhooks are commonly useful for payment events, order updates, Git events, shipping updates, notifications, and many other automated processes.

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6. SOAP API

Another important API technology is SOAP.

The word is SOAP, not “shop.” It stands for Simple Object Access Protocol.

SOAP is a protocol used for structured communication between applications.

It is strongly associated with XML-based messaging.

SOAP has historically been widely used in areas where strict contracts, standardization, and enterprise requirements are important.

Examples can include:

• Banking systems
• Insurance platforms
• Government systems
• Enterprise software
• Older business applications
• Financial services

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How SOAP Works

SOAP messages are usually built using XML.

A SOAP message commonly contains a structured envelope.

A simplified SOAP structure looks like this:

<soap:Envelope>
  <soap:Header>
    <!-- Optional information -->
  </soap:Header>

  <soap:Body>
    <!-- Request information -->
  </soap:Body>
</soap:Envelope>

The envelope defines the overall SOAP message.

The header can contain additional information such as authentication or other processing details.

The body contains the actual request or response.

SOAP also has a broader ecosystem of standards for areas such as security, reliability, transactions, and addressing.

One example is WS-Security, which provides standards for securing SOAP messages.

SOAP can therefore be useful when an organization needs formal contracts and enterprise-grade standards.

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REST vs GraphQL vs gRPC vs WebSocket vs Webhook vs SOAP

Now let’s compare the major types of APIs in simple language.

API Type	Main Purpose	Common Use
REST	Standard web communication	Websites and mobile apps
GraphQL	Request specific data	Flexible applications
gRPC	Fast service-to-service communication	Microservices
WebSocket	Real-time two-way communication	Chat and live tracking
Webhook	Event-based notifications	Payments and automation
SOAP	Structured enterprise communication	Banking and enterprise systems

Each technology solves a different problem.

There is no single API style that is perfect for every application.

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When Should You Use REST API?

REST can be a good choice when you need a standard API for:

• Web applications
• Mobile applications
• Public APIs
• CRUD operations
• Simple backend communication

For many traditional applications, REST is an easy and practical starting point.

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When Should You Use GraphQL?

GraphQL can be useful when:

• The client needs different fields at different times.
• A page needs data from several related resources.
• You want clients to control the fields they receive.
• You need flexible data queries.

It is particularly useful for complex front-end applications.

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When Should You Use gRPC?

gRPC is a strong choice when:

• You have a microservices architecture.
• Services need fast communication.
• Performance is important.
• You control both sides of the communication.
• You want strongly defined service contracts.

For public browser-facing APIs, REST or GraphQL may often be simpler, while gRPC is especially powerful for internal service communication.

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When Should You Use WebSocket?

Use WebSocket when your application needs real-time updates.

Good examples include:

• Chat applications
• Online games
• Live tracking
• Real-time dashboards
• Trading interfaces
• Live notifications

The main idea is that communication remains active instead of repeatedly creating new connections.

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When Should You Use Webhooks?

Webhooks are useful when you want one system to automatically notify another system after an event happens.

For example:

Payment completed → Send webhook

Order shipped → Send webhook

Git push received → Send webhook

User subscription changed → Send webhook

This is especially useful for automation and event-driven applications.

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When Should You Use SOAP?

SOAP can still make sense when working with:

• Large enterprise systems
• Banking applications
• Insurance systems
• Government applications
• Legacy software
• Systems requiring formal contracts and established security standards

SOAP may appear more complex than REST, but its standards and structured design can be valuable in certain enterprise environments.

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Real-Life Example: Food Delivery Application

Let’s put everything together using a food delivery application.

Suppose you open an online food delivery app.

REST

REST may be used to retrieve restaurants, create orders, update account details, and manage other standard resources.

GraphQL

GraphQL could be used by a complex mobile screen that needs the customer’s name, rewards, saved address, recent orders, and recommendations.

gRPC

Internally, the payment service, order service, restaurant service, and delivery service could communicate using gRPC.

WebSocket

WebSocket could be used for real-time delivery tracking or chat.

Webhook

The payment provider could send a webhook when a payment succeeds.

SOAP

A connected banking or enterprise system may use SOAP where formal XML-based communication is required.

This example shows why there are different types of APIs. Each technology has a different job.

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What Is the Difference Between API and API Type?

It is important to understand the difference.

An API is the general concept of a communication interface between software systems.

An API style or technology describes how that communication is designed and implemented.

REST, GraphQL, gRPC, WebSocket, Webhook, and SOAP are different approaches with different characteristics.

When developers choose an API technology, they consider things such as:

• Performance
• Security
• Scalability
• Data requirements
• Real-time communication
• Complexity
• Team expertise
• System architecture

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Are APIs Secure?

APIs need proper security because they often expose sensitive data or important functionality.

Common API security practices include:

HTTPS

HTTPS encrypts communication between the client and server and helps protect data while it travels across the network.

Authentication

Authentication verifies who is making the request.

Examples include:

• API keys
• Sessions
• OAuth
• Tokens

Authorization

Authorization decides what the authenticated user is allowed to do.

For example, a normal customer may be allowed to view their own order but not another customer’s order.

Input Validation

The server should validate incoming data and reject invalid or dangerous input.

Rate Limiting

Rate limiting can restrict how many requests a client can make within a certain period.

Logging and Monitoring

Applications should monitor API activity to identify unusual behavior, errors, and possible attacks.

Security is important for every API style, whether it is REST, GraphQL, gRPC, WebSocket, Webhook, or SOAP.

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Advantages of Using APIs

APIs provide many benefits to modern software development.

Easy Communication

APIs allow different systems to communicate in a standard way.

Reusability

A backend service can be used by websites, mobile apps, and other clients.

Faster Development

Developers can use existing services instead of building everything from zero.

Integration

APIs make it easier to connect different platforms.

Scalability

Large applications can divide functionality into separate services and communicate through APIs.

Automation

APIs and webhooks can allow different systems to work together automatically.

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Common Interview Question: What Are the Types of APIs?

A common interview question is:

“What are the different types of APIs?”

A simple answer could be:

REST is commonly used for standard web and mobile application communication. GraphQL allows clients to request specific data. gRPC is often used for fast communication between microservices. WebSocket is used for real-time two-way communication. Webhooks are used for event-based notifications, and SOAP is an XML-based protocol commonly found in enterprise environments.

This answer demonstrates that you understand not only the names but also the use cases.

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Final Thoughts on Types of APIs

Understanding the different types of APIs is very important for anyone learning web development, backend development, mobile development, cloud computing, or software architecture.

REST is one of the most common choices for standard web APIs.

GraphQL provides flexible data fetching.

gRPC is powerful for high-performance communication between services.

WebSocket is useful when real-time communication is required.

Webhooks are excellent for event-based notifications.

SOAP remains important in many enterprise and legacy environments where formal contracts and standards are required.

The most important thing is not simply memorizing the names. You should understand why and when each API technology is used.

For example, a simple website may work perfectly with REST. A complex application that needs flexible data fetching may benefit from GraphQL. A microservice architecture may use gRPC internally. A live chat application may use WebSocket. A payment system can send webhooks when transactions change, while an enterprise banking integration may still use SOAP.

Once you understand these differences, API concepts become much easier.

In simple words, remember this:

REST = Standard web communication

GraphQL = Request the data you need

gRPC = Fast service-to-service communication

WebSocket = Real-time communication

Webhook = Automatic event notification

SOAP = Structured enterprise communication

These are some of the most important types of APIs, and learning their differences can help you answer technical interview questions and make better decisions when designing software applications.