What Is a REST API? Key Concepts, Best Practices, and Benefits in 2025

What is a REST API?

A REST API, short for Representational State Transfer Application Programming Interface, is a method that allows software systems to communicate over the internet using standard HTTP protocols. Designed with specific principles and conventions, REST APIs are lightweight, scalable, and easy to implement. They are a cornerstone of web development, enabling seamless interaction between clients (such as web browsers, mobile apps, or other servers) and backend servers.

Read more: What is an API? How APIs Work, Simply Explained

History of REST APIs

Before REST gained prominence, developers relied heavily on SOAP (Simple Object Access Protocol) for API integrations. However, SOAP was often criticized for its complexity and challenging debugging process. To address these issues, Roy Fielding and a team of developers introduced REST, transforming how APIs were designed and utilized.

Here’s a brief history of REST APIs:

• Before REST: Developers used SOAP, crafting XML documents with Remote Procedure Calls (RPCs) in the body. These documents were sent to a specific endpoint using the POST method.
• 2000: Roy Fielding and his team established REST by defining a universal set of constraints. This standardization made it easier for servers to interact with one another.
• 2002: eBay introduced its REST API, enabling external sites to connect to its platform, which inspired Amazon to launch its API the same year.
• 2004–2006: Flickr debuted its RESTful API in 2004, allowing bloggers to integrate images into their websites and social media. By 2006, both Facebook and Twitter launched their APIs to accommodate growing developer interest and avoid unauthorized “Frankenstein” APIs.
• 2006–Present: RESTful APIs have become the default for developers to integrate functionalities into websites and apps. Tools like Postman have further streamlined API creation and collaboration, accelerating development.

What are the main elements of RESTful API?

REST APIs rely on three primary elements:

1. Client: The application or software that sends a request for resources.
2. Server: The backend application that manages resources and responds to client requests.
3. Resource: The data or content (e.g., text, images, videos) controlled by the server and made accessible to the client.

To request a resource, the client sends an HTTP request to the server. These requests typically include four main components:

HTTP Method: Specifies the intended action for the resource. Common methods include:

• POST: Create a new resource.
• GET: Retrieve an existing resource.
• PUT: Update an existing resource.
• DELETE: Remove a resource.

Endpoint: Indicates the location of the resource, typically expressed as a Uniform Resource Identifier (URI) or a URL for internet-accessible resources.

Header: Provides essential details for executing the request, such as authentication credentials, encryption keys, server information, and the preferred response format.

Body: Contains data sent to or from the server, such as new information to add via a POST or PUT request.

HTTP Methods and CRUD Operations

When the client sends a request, the server processes it and returns a response. This response includes the requested data in a format like XML, JSON, or plain text. Additional details, such as error codes, timestamps, or processing instructions, may also be included. Importantly, the self-descriptive nature of these calls ensures that all necessary information for interpreting and processing the request is embedded within the communication itself.

Ways to use REST APIs

APIs are integral to any application that connects with another system. In today’s business landscape, they enable companies to scale operations, enhance customer experiences, and reduce the need for extensive development resources by allowing seamless communication with third-party applications through public APIs.

Common Use Cases for REST APIs

• Cloud Computing: Facilitating interaction between cloud services.
• Microservices: Enabling communication among various microservices.
• Web Services: Supporting web-based applications.

Marketing is one sector that significantly benefits from REST APIs. As digital marketing becomes increasingly vital for customer engagement, effective integration between marketing tools and software is essential. Here are some ways APIs bolster marketing efforts:

• Automation: Tools like CRMs and email marketing platforms improve efficiency by automating tasks such as data entry, allowing teams to focus on strategic initiatives. REST APIs facilitate integration across diverse software solutions.
• Data Analytics: Integrating analytics from multiple sources—like websites and social media—provides marketers with insights to make informed decisions and refine strategies based on comprehensive data analysis.
• Email Marketing: Email APIs enable the automated sending of transactional messages (e.g., order confirmations) by interfacing with email servers to keep customers informed about their transactions.
• Social Media Integration: Social media APIs help collect customer metrics and allow for embedding feeds directly onto websites. They can also integrate with CRMs to enhance campaign personalization.
• Enhanced Customer Experience: APIs simplify adding features like multiple payment options (e.g., PayPal or Google Pay) to e-commerce sites without extensive coding, improving user functionality and satisfaction.

REST design principles

At its core, an API serves as a conduit that allows one application or service to access resources from another. The application accessing these resources is termed the client, while the application housing the resources is known as the server. Unlike APIs such as SOAP or XML-RPC, which enforce rigid structures on developers, REST APIs can be constructed using nearly any programming language and can accommodate various data formats. The only stipulation is adherence to the following six REST design principles, often referred to as architectural constraints.

Uniform Interface

Requests made to the same resource should maintain a consistent format, regardless of their origin. A REST API must guarantee that each piece of data—such as a user’s name or email address—is associated with a single unique resource identifier (URI). Resources should be appropriately sized and contain all necessary information for the client.

Client-Server Decoupling

In designing REST APIs, it is crucial that client and server applications operate independently. The client should only need to know the URI of the resource it seeks and should not engage with the server in any other manner. Conversely, the server should not alter the client application beyond providing the requested data via HTTP.

Statelessness

REST APIs are designed to be stateless, meaning each request must carry all information required for processing. This approach eliminates the need for server-side sessions, as servers are prohibited from retaining any data related to client requests.

Cacheability

Resources should be cacheable whenever feasible, either on the client side or server side. Responses from the server must indicate whether caching is permissible for the resource provided. This practice aims to enhance client performance and improve server scalability.

Layered System Architecture

REST APIs function through multiple layers of communication. It is important not to assume direct connectivity between client and server applications; instead, various intermediaries may exist within this communication framework. The design of REST APIs should ensure that neither party can discern whether they are interacting directly with the end application or an intermediary.

Code on Demand (Optional)

While REST APIs typically transmit static resources, there are instances where responses may include executable code (such as Java applets). In these cases, such code should only be executed upon request.

Structure of REST Responses

When responding to requests, servers do not send back the actual resource but rather its representation—a machine-readable description reflecting its current state. The same resource can be represented in various formats, with XML and JSON being among the most common.

Whenever applicable, servers include hyperlinks or hypermedia in their responses that connect to other related resources. This approach provides clients with guidance on potential subsequent actions and further requests they can initiate.

Why Use REST APIs?

The REST framework, conceptualized by computer scientist Roy Fielding in 2000, fundamentally influences how we access, modify, and share content online. Major web and cloud platforms like Facebook, YouTube, Twitter, and Google utilize REST APIs in their applications.

So, what makes REST so appealing? Essentially, it provides an effective architecture for web applications. Here are the primary advantages of using this type of API:

• Flexibility: REST APIs can accommodate various request types and transmit data in multiple formats.
• Scalability: They are designed to facilitate communication between any two software components, regardless of their size or capabilities. As a web application expands and incorporates additional resources, its REST API can efficiently manage the growing volume and diversity of requests.
• Utilization of Existing Web Technologies: Building and using REST APIs is relatively straightforward since they leverage standard web technologies. To request a resource through a REST API, you simply need to provide its URL.

What are the Benefits of RESTful API?

REST APIs have surged in popularity due to the significant benefits they offer to developers and organizations alike, including:

• Simplicity: By employing standard HTTP methods—GET, PUT, POST, and DELETE—REST APIs are easy to design, implement, and utilize.
• Independence: Developers benefit from platform independence as they can create REST APIs using nearly any programming language. These APIs work seamlessly with various client devices, including traditional web browsers, mobile devices, and IoT devices.
• Versatility: Supporting numerous data formats such as JSON, XML, and plain text allows developers to choose the format that best meets client needs and server capabilities.
• Scalability: The stateless design of REST APIs promotes horizontal scaling, enabling multiple API calls to run simultaneously to manage substantial loads.
• Cacheability: REST APIs support caching mechanisms that allow data to be stored locally. This can enhance server response times and potentially reduce the need for repeated API calls if the required data is already available on the client side.
• Security: Calls and data exchanges can be secured using Open Authorization (OAuth) for authentication and Secure Sockets Layer/Transport Layer Security (SSL/TLS) for encryption.
• Compatibility: Effective versioning practices enable developers to evolve APIs over time while maintaining backward compatibility and supporting legacy features for existing clients.

Common REST API challenges

While REST APIs offer many advantages, they also present certain challenges:

• Endpoint Consistency: Maintaining consistent endpoint paths that adhere to common web standards can be complex.
• API Versioning: It’s crucial that endpoint URLs remain valid when used internally or with other applications.
• Response Times and Data Volume: Over time, the amount of returned resources may increase, leading to longer load times and response delays.
• Navigation Paths and Input Locations: Utilizing URL paths for input parameters can complicate determining valid URL spaces.
• Security Management: Numerous security issues must be addressed, including implementing HTTPS, blocking unauthorized IP addresses, validating URLs, managing payload sizes, monitoring requests, and investigating failures.
• Authentication Methods: Familiarity with common authentication techniques—such as HTTP basic authentication (which uses a base64-encoded username and password), API keys, JSON Web Tokens (JWT), and OAuth 2.0—is necessary for effective security management.
• Data Requests: Requests may contain excessive data or metadata or require multiple requests to retrieve all necessary information. Adjustments can be made to optimize this process.
• Error Handling: Utilizing standard HTTP error codes is common practice; however, distinguishing between successful responses may require parsing the body or checking for errors.
• API Testing Complexity: Setting up tests can be a lengthy process with various challenges involved. Testing can also be conducted via command-line tools like cURL. Challenges include initial setup difficulties, schema updates, parameter combinations, sequencing API calls, validating parameters, and ensuring system integration.

Final thoughts on REST APIs

This article has provided a comprehensive overview of what a REST API is, how it operates, its applications, and more. You have also learned about the distinctions between SOAP and REST. While understanding APIs can be daunting for new developers, resources like The Freedom of Work’s public REST API collection and glossary can help you expand your knowledge of various REST APIs.