4 Major Types of API Architectural Styles

APIs connect applications, enabling them to communicate seamlessly across systems, platforms, and devices. But not all APIs are built the same way. The architectural style behind an API determines how data is structured, transmitted, and consumed, which ultimately affects performance and scalability.

Developers must choose the right architectural style to match specific project goals. Whether you’re designing a simple data-sharing service, a real-time chat system, or a complex enterprise integration, the API style you choose directly impacts maintainability and performance.

In this article, I’ll explore four major API architectural styles that dominate modern software design , SOAP, REST, GraphQL, and WebSockets. We’ll look at what each style is, how it works, and when to use it, so you can make smarter decisions in your next project.

1. SOAP (Simple Object Access Protocol)

What It Is

SOAP is one of the earliest and most formalized web service protocols, developed by Microsoft in the late 1990s. It defines a strict messaging structure based on XML, making it ideal for enterprise systems that require high security, reliability, and standardized communication.

SOAP isn’t just an architectural guideline, it’s a protocol. This means it comes with defined rules on how messages are formatted and transmitted. It operates primarily over HTTP but can also use other protocols like SMTP or TCP.

How It Works

SOAP APIs send and receive XML-based messages called envelopes. Each envelope contains:

• A Header (for metadata, authentication, etc.)
• A Body (where the main data resides)

A typical SOAP request looks like this:

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
<soapenv:Header/>
<soapenv:Body>
<getUserDetails>
<userId>12345</userId>
</getUserDetails>
</soapenv:Body>
</soapenv:Envelope>

SOAP messages rely on a WSDL (Web Services Description Language) file that defines the available operations, data types, and message structures providing a contract between client and server.

SOAP also supports built-in features like:

• WS-Security for authentication and message integrity
• ACID transactions
• Retry logic and error handling via standardized fault elements

When to Use SOAP

Use SOAP when:

• You’re building enterprise-grade applications (e.g., banking, healthcare, or telecom systems).
• Security and reliability are non-negotiable (WS-Security and WS-ReliableMessaging support).
• You need strict contracts and strong typing through WSDL.

Avoid SOAP when:

• You want lightweight, flexible APIs that integrate easily with web and mobile apps.
• JSON-based data formats are preferred.

2. REST (Representational State Transfer)

What It Is

REST, introduced by Roy Fielding in 2000, is an architectural style, not a protocol. It’s built on a set of principles that promote simplicity, scalability, and statelessness. REST APIs are designed around resources (e.g., users, products, orders) that are accessed via standard HTTP methods.

REST became the de facto standard for modern web APIs because of its simplicity, performance, and alignment with the web’s existing architecture.

How It Works

In REST, every resource is identified by a unique URL. Interactions happen through HTTP methods:

• HTTP Method
• Action

Example Endpoint
GET
Retrieve data
/api/users
POST
Create a resource
/api/users
PUT
Update a resource
/api/users/123
DELETE
Remove a resource
/api/users/123

REST typically exchanges data in JSON, though XML and other formats are possible. Each request is stateless, meaning the server doesn’t store client context between requests.

Example REST request:
GET /api/users/123 HTTP/1.1
Host: example.com
Accept: application/json

Response:
{
"id": 123,
"name": "Victoria",
"role": "Technical Writer"
}

When to Use REST

Use REST when:

• You need simple, scalable APIs for web, mobile, or IoT.
• You want broad compatibility. REST works almost anywhere.
• You value human-readable and lightweight communication.

Avoid REST when:

• Your client needs complex querying or nested data in a single request (GraphQL may be better).
• You require real-time data or continuous streaming (WebSockets fit better).

3. GraphQL

What It Is

Developed by Facebook in 2012 and open-sourced in 2015, GraphQL is a query language for APIs that gives clients the power to request exactly the data they need, nothing more, nothing less.

Unlike REST, where multiple endpoints serve different resources, GraphQL typically exposes a single endpoint that handles all data queries through flexible schemas.

How It Works

GraphQL APIs revolve around three main concepts:

• Schema: Defines types and relationships between data.
• Query: The client’s request for specific data.
• Resolver: The function that fetches the requested data.

Example query:
{
user(id: 123) {
name
posts {
title
likes
}
}
}
Response:
{
"user": {
"name": "Victoria",
"posts": [
{ "title": "Understanding API Architecture", "likes": 42 }
]
}
}

The key feature here is data efficiency, the client decides the structure of the response. This avoids over-fetching (getting too much data) and under-fetching (needing multiple calls to get related data).
GraphQL also supports:

• Mutations (for data creation and updates)
• Subscriptions (for real-time updates)
• Strong typing for predictable data responses

When to Use GraphQL

Use GraphQL when:

• You want efficient data fetching in apps with complex data relationships.
• Your frontend is highly dynamic, like mobile or dashboard apps.
• You want API evolution without breaking changes (GraphQL schemas handle versioning gracefully).

Avoid GraphQL when:

• You’re building simple APIs with limited data complexity.
• You need built-in caching and performance (requires extra setup).
• You prefer strict standards and tooling (REST still leads here).

4. WebSockets

What It Is

WebSockets are a communication protocol designed for real-time, bidirectional data exchange between clients and servers. Unlike REST or GraphQL, which are request-response based, WebSockets maintain a persistent connection that allows both parties to send and receive messages anytime.

This makes WebSockets ideal for chat applications, live dashboards, gaming platforms, and any scenario where instant updates are crucial.

How It Works

Once a WebSocket connection is established, it upgrades a standard HTTP connection into a persistent TCP connection using a “handshake.”

Example:
GET /chat HTTP/1.1
Host: example.com
Upgrade: websocket
Connection: Upgrade

After the handshake, both the client and server can send data freely:

Client → Server: Send messages (e.g., new chat message)
Server → Client: Push updates instantly (e.g., notifications, game scores)

Unlike REST or GraphQL, there’s no repeated connection setup or HTTP overhead, making WebSockets extremely fast for continuous communication.

When to Use WebSockets

Use WebSockets when:

• You need real-time communication (e.g., chat, trading dashboards, multiplayer games).
• Low latency is essential.
• The server must push data without client requests.

Avoid WebSockets when:

• Your application doesn’t require continuous or real-time interaction.
• You need simple CRUD operations . REST or GraphQL are simpler to maintain.
• You’re targeting environments where persistent connections are restricted.

Conclusion

APIs form the foundation of modern software systems, shaping how applications communicate, scale, and evolve across platforms. Each architectural style, whether SOAP, REST, GraphQL, or WebSockets, offers unique strengths suited to different needs. SOAP provides the reliability and structure essential for enterprise-level systems, REST offers simplicity and scalability for web and mobile applications, GraphQL introduces flexibility and efficiency for complex, data-driven environments, and WebSockets enable real-time, bidirectional communication for interactive applications. Understanding these architectural differences allows developers, architects, and technical writers to design and document APIs that are not only functional but purpose-built for performance and longevity.