What Is REST API? A Practical Guide

APIs are the invisible backbone of modern software. They let different applications communicate, share data, and evolve independently. One of the most widely used API styles is the REST API. If you’ve worked with integrations, cloud services, or even mobile apps, chances are you’ve interacted with a REST API, directly or indirectly.

But what is REST API, exactly? Why has it become the standard choice for web services? And how do developers design, secure, and use RESTful APIs in practice?

This guide will explain in a practical way:

• What REST APIs are,
• The REST architectural style,
• REST API key components,
• Authentication methods,
• Common use cases,
• The benefits and limitations of them

By the end, you’ll understand why REST is considered the foundation of modern system architecture - and what best practices help API developers build reliable, scalable, and secure RESTful web services.

What Is REST API?

A REST API (short for Representational State Transfer API) is a type of application programming interface (API) that follows the REST architectural style.

Unlike SOAP, which is a strict communication protocol, REST is an architecture for designing web services. It defines a set of principles and constraints that ensure systems can share data efficiently and evolve without being tightly coupled.

In simple terms, a REST API is a web API that lets a client (such as a mobile app, web application, or another server) interact with a server using standard HTTP methods like GET, POST, PUT, and DELETE.

REST APIs power most of today’s cloud services, mobile apps, and integrations. From logging into your email, to booking a ride, to syncing data between apps with a tool like Getint, behind the scenes, client-server interactions often happen through RESTful APIs.

Core Principles of REST

To be considered RESTful, an API must follow six architectural constraints defined by REST’s creator, Roy Fielding. These principles shape how the client and server interact.

Client-server architecture

REST APIs are built on a client-server architecture. The client (e.g., a mobile app) handles client functionality such as user interface and user interactions. The server handles server components like business logic, databases, and resource storage.

This separation allows client and server to evolve independently. For example, a server can be migrated from one database to another without affecting the client, as long as the uniform interface of the API stays the same.

Statelessness

Each REST API request must contain all the information required for the server to process it. The server does not store client context between requests.

This stateless design improves scalability - any server in a cluster can handle a request without needing prior knowledge. It also makes failures easier to recover from.

Cacheable data

REST allows responses to be cacheable. A server response can include headers that tell the client or intermediary systems whether data may be reused. Proper caching improves performance by reducing duplicate calls, lowering latency, and minimizing load on servers.

Uniform interface

The uniform interface principle is what gives REST APIs their predictability. It includes:

• Resource identification - each resource is uniquely identified by a Uniform Resource Identifier (URI), such as /users/123.
• Resource representation - resources are transferred in a chosen format (commonly JSON or XML).
• Self-descriptive messages - requests and responses include enough information for clients and servers to understand them independently.
• Hypermedia as the Engine of Application State (HATEOAS) - responses can contain links to related resources, guiding clients dynamically.

Layered system

RESTful APIs support a layered system, where requests may pass through multiple layers, such as load balancers, API gateways, or proxies - before reaching the final server.

This multiple layers design increases scalability and security. Clients do not need to know whether they’re talking to the end server or an intermediary.

Code on demand (optional)

In some cases, servers may extend client functionality by sending executable code (e.g., JavaScript). This optional constraint allows clients to adapt dynamically, though most REST APIs don’t rely heavily on it.

Key Components of a REST API

Understanding REST means understanding its core building blocks: resources, URIs, HTTP methods, and responses.

Resources and URIs

In REST, everything is treated as a resource. A resource could be a user, a task, an order, or even an image.

Each resource is identified by a specified URL (or URI). For example:

• /users → a collection of users
• /users/123 → a single user resource
• /users/123/orders → a parent resource (user) with a child (orders)

HTTP methods

RESTful APIs use standard HTTP methods to manipulate resources:

• GET – retrieve data (safe and cacheable)
• POST – create a new resource (not idempotent; the same POST request may create multiple items)
• PUT – replace an entire resource (idempotent; the same PUT request multiple times yields the same result)
• PATCH – update part of a resource
• DELETE – remove a resource

These methods map to CRUD operations: Create, Read, Update, Delete.

Requests and Responses

A typical RESTful API request consists of:

• Endpoint (URI) - the resource address
• HTTP method - GET, POST, PUT, DELETE, PATCH
• Headers - metadata (e.g., Content-Type, Authorization, caching)
• Query parameters - filters, pagination, or search terms
• Request body - data sent in POST/PUT/PATCH requests

A server response typically includes:

• HTTP status codes - e.g., 200 OK, 201 Created, 400 Bad Request, 404 Not Found, 500 Internal Server Error
• Response body - a representation of the resource (often JSON)
• Response headers - metadata such as Content-Type or caching instructions

This request-response cycle ensures self-descriptive messages and predictable API responses.

REST API Authentication

Because REST is stateless, every request must include authentication credentials. Common methods include:

• API keys - simple tokens passed in headers or query parameters.
• Bearer tokens - random strings or JWTs passed as Authorization: Bearer <token>.
• OAuth 2.0 - a secure, delegated authentication framework for user-based access.

Using appropriate authentication ensures only authorized API consumers can send data, retrieve data, or manipulate resources.

Always enforce HTTPS for REST APIs to ensure credentials remain secure.

REST API vs SOAP API

SOAP (Simple Object Access Protocol) was once the dominant standard for web services, but REST has overtaken it in popularity.

In short: REST is simpler, faster, and more flexible, while SOAP remains in use in industries needing strict contracts or advanced security features like banking, healthcare.

Common Use Cases of REST APIs

REST APIs are everywhere. Some popular scenarios include:

• Web and mobile applications – frontend apps call RESTful APIs to fetch and update data.
• Cloud services – platforms like AWS, Azure, and Google Cloud expose REST APIs for automation.
• Microservices – REST allows different software systems to integrate within modern architectures.
• IoT devices – lightweight clients (sensors, thermostats) use REST to share data with servers.
• Business integrations – tools like Getint use REST to sync Jira, ServiceNow, Azure DevOps, and other platforms seamlessly - through REST API, we efficiently fetch data that needs to be synchronized between various platforms.

Benefits of REST APIs

REST APIs have several advantages:

• Simplicity - easy to learn and implement, thanks to HTTP and JSON.
• Scalability - stateless design and caching support high loads.
• Flexibility - clients and servers can evolve independently.
• Interoperability -works across different programming languages and systems.
• Performance - lightweight compared to SOAP or other protocols.

Limitations of REST APIs

RESTful APIs are widely adopted, but they do have some shortcomings.

• One frequent issue is data fetching - endpoints often return a fixed response, which can lead to over-fetching(receiving more data than needed) or under-fetching (having to make several requests to gather enough information). Both scenarios can slow down applications and increase unnecessary traffic.
• Another limitation is that REST lacks a strict contract. Unlike SOAP, which enforces structure through WSDL, REST APIs depend on documentation and conventions. This flexibility is useful, but it also means API consumers may encounter inconsistencies or breaking changes if the API isn’t carefully maintained.
• Finally, REST’s request-response model makes it less suitable for real-time interactions such as chat or live dashboards. It works best for traditional client-server interactions, but streaming scenarios usually require complementary technologies like WebSockets.

These drawbacks don’t make REST a poor choice - far from it. They simply highlight the importance of thoughtful design. Which brings us to the next point: what makes a REST API not just functional, but practical, secure, and easy to use?

Best Practices for Implementing REST APIs

When designing or using RESTful web services, following best practices ensures the application programming interface is predictable, secure, and scalable. From how resources are named to how authentication is handled, these guidelines help developers design APIs that are both powerful and user-friendly.

1. Use clear resource naming – /users/123/orders is better than /getUserOrders.

1. Follow HTTP methods – GET for reads, POST for creates, PUT/PATCH for updates, DELETE for removals.
2. Return proper status codes – don’t return 200 OK for errors. Use 400, 401, 404, 500 appropriately.
3. Secure with authentication – use API keys, tokens, or OAuth2, and always enforce HTTPS.
4. Support filtering and pagination – let clients use query parameters like ?page=2&limit=50.
5. Provide consistent response formats – Stick to one appropriate representation format (usually JSON).
6. Implement rate limiting – protect against abuse and ensure fair usage.
7. Document your API – use tools like OpenAPI/Swagger to describe endpoints and responses clearly.

By following these rules, API developers create RESTful APIs that are easy to integrate, secure, and reliable.

Final Thoughts

So, what is REST (representational state transfer) API? It’s a design style for building APIs that emphasizes resources, uniform interface, and stateless communication. RESTful APIs allow different software systems to communicate, share data, and evolve independently, all through the simplicity of the HTTP protocol.

Whether you’re building a mobile app, connecting cloud services, or integrating Jira with ServiceNow or other tools, RESTful APIs provide the reliable foundation for modern interactions with servers.

While newer technologies like GraphQL and gRPC are emerging, REST remains the most widely used approach for exposing and consuming APIs. Its balance of simplicity, scalability, and flexibility makes it the go-to solution for both API developers and API consumers.

At Getint, we see REST APIs as the key enabler of integrations, helping teams connect tools like Jira, ServiceNow, Azure DevOps, and many more applications without friction.