What are REST APIs? HTTP API vs. REST API

REST APIs are a common web development topic that enables clients and servers to communicate with each other. Ever wondered why everyone talks about REST APIs? Or confused by how they relate to HTTP APIs? Understanding what REST APIs are and how they differ from other HTTP APIs is crucial for developers looking to build scalable and efficient applications.

In this blog, we’ll learn about REST APIs by explaining what they are, how they differ from other HTTP APIs, and when to use them. By the end, you’ll gain a solid understanding of these architectural principles and their real-world applications. We’ll also explore alternative API architectures like GraphQL and gRPC to give you a comprehensive understanding of the API landscape.

What is an HTTP API?#

An HTTP API is an Application Programming Interface that uses the Hypertext Transfer Protocol (HTTP) for communication between clients and servers. It provides a set of rules and endpoints (URLs) that applications use to exchange data or request services.

The communication follows the HTTP request-response model: a client (such as a web browser or application) sends an HTTP request to a server, which processes it and sends back an HTTP response containing the requested data or the result of the operation. HTTP APIs are commonly used in web and mobile applications to enable integration and interaction between different systems.

For example, consider the process of scheduling a Zoom meeting directly within your Google Calendar. When you create a new calendar event and choose to add a Zoom meeting, Google Calendar sends an HTTP request to Zoom’s API. The request may contain details like the event time, participants, and authentication information. Zoom’s API processes the request, creates the meeting, and responds to Google Calendar with the meeting details (e.g., the Zoom link, meeting ID, and password). Google Calendar then embeds this information directly into your event, eliminating the need to manually copy and paste meeting details. This seamless interaction between Zoom and Google Calendar is possible because HTTP APIs enable efficient and standardized communication between the two services.

What is a REST API?#

Now that we understand HTTP APIs as the foundation, let’s explore how REST builds upon these principles to offer a more structured and scalable approach. Representational State Transfer (REST) is an architectural style that defines a set of constraints for creating web services. It was developed by Roy Fielding in 2000 and has led to a growing collection of RESTful web services that follow the REST principles. It is the most prevalent type of HTTP API due to its simplicity and scalability. REST APIs are widely adopted due to their simplicity and reliance on standard HTTP communication methods, making them more straightforward compared to older and more complex protocols like CORBA, RPC, or SOAP.

REST provides a standardized approach to structuring APIs. It leverages HTTP methods such as GET, POST, PUT, and DELETE to perform operations like Create, Read, Update, and Delete (CRUD). REST emphasizes the simplicity of interfaces, ensuring that interactions between clients and servers remain stateless and uniform.

Requirements for an API to be a REST API#

Not all HTTP APIs are REST APIs. The API needs to meet the following architectural requirements to be considered a REST API:

1. Uniform interface: This is the defining feature of REST. It ensures that resources are consistently represented and accessed through standard HTTP methods (e.g., GET /users retrieves users, POST /users creates a new user). This uniformity simplifies interactions and increases interoperability. Think of it as a universal language for your API, where everyone knows how to ask for something and get a predictable response.

2. Statelessness: REST APIs require that the client’s requests to the server contain all the information required to process them. Among requests, the client state is not retained by the server, making the system easier to scale and more resilient. Think of it like a fast-food drive-thru. Each customer provides all the necessary details (order, payment) in one go. The restaurant doesn’t remember past customers; it only focuses on the current request.

3. Cacheable: Responses from the server must be explicitly marked as cacheable or non-cacheable. Cacheable responses allow clients to improve performance by reusing data, while non-cacheable data prevents clients from using stale information.

4. Client-server architecture: There should be a separation between the server that offers a service and the client that consumes it. This separation allows for independent updates and scalability of the server and the client if required. To better understand this, think of a restaurant where the kitchen (server) prepares the food while the customers (clients) order and consume it. The kitchen doesn’t dictate how or where customers enjoy their meals, and customers don’t interfere with the kitchen operations.

5. Layered system: REST systems are built with a layered architecture, where each component interacts only with the next immediate layer. This abstraction supports adding features like proxies, gateways, or load balancers for improved scalability, security, and performance. For example, a content delivery network (CDN) sits between the client and the server, caching static assets like images or stylesheets to reduce the server’s load while speeding up client-side performance.

6. Code on demand: Servers can provide executable code or scripts for clients to execute in their context. This constraint is the only one that is optional.

These constraints combine to create an application with strong boundaries and a clear separation of concerns.

How do REST APIs work?#

The client initiates a communication by sending an HTTP request to the server. The server receives the request and processes the action using the HTTP method. After processing the request, the server sends back an HTTP response to the client. The client manipulates or displays the data and notifies the server of any state changes.

Just like HTTP, REST APIs use methods to define the type of request that is sent to the server.

• GET: Retrieves the data entry at a given endpoint.

• POST: Creates new data entry in the database.

• PUT: Updates an existing data entirely.

• PATCH: Updates part of a data entry.

• DELETE: Deletes a data entry.

Here’s an example of a RESTful API design completing a request/response loop. The client requests to retrieve a customer’s details from the server:

The server responds with the customer’s details:

When to use REST APIs#

REST APIs are great for building general-purpose applications—particularly for CRUD (Create, Read, Update, Delete) operations— while ensuring scalability in the future. For example, REST APIs are commonly used in mobile apps or public APIs for SaaS platforms like payment gateways or weather services, where scalability and wide compatibility are critical.

REST APIs are inherently decoupled from your client-side technology, meaning your application can work well on iOS, browsers, or devices of the future with minimal difficulty. As a result, you can build your app with fewer concerns about being bound to particular client-side stacks and can focus on developing the app itself. RESTful APIs are, therefore, more scalable and have a longer lifespan.

Caching also allows REST APIs to be more scalable by reducing the number of requests that the server needs to process for an in-demand resource. For instance, an API delivering weather updates can cache responses for high-traffic cities, reducing redundant requests and saving server resources. By caching the response and sending the cached response instead of reprocessing the request, RESTful services can process more requests with fewer resources.

When not to use REST#

While REST’s stateless architecture offers significant advantages, it also has limitations that make it less suitable for certain use cases. Statelessness simplifies server-side scalability and flexibility, as the server does not retain the client state between requests. However, this also means that every request must include all the necessary information to complete the operation. For systems with frequent, complex interactions, like batch processing systems where requests need to share context, this can lead to larger payloads and redundant data transmission, which may impact performance.

With REST APIs, clients may receive too much or too little data for a request. They may also not be the best choice for applications requiring real-time, bidirectional communication or highly interactive data queries. For example, GraphQL is often preferred for applications with dynamic and complex data-fetching needs, like e-commerce platforms requiring flexible product filtering, whereas gRPC excels in low-latency, high-performance scenarios with streaming or RPC-style operations.

It’s also important to note that you don’t have to strictly adhere to REST architecture in all situations to gain the benefits. Using the principles of REST when they’re better suited is better than twisting an RPC-style request into a REST-style.

Types of APIs#

HTTP APIs can be designed following different architectural styles. The most common ones are as follows:

1. GraphQL#

GraphQL is a query language for APIs developed by Facebook. It’s open-source and designed to hold data in a tree structure. The main difference is that the GraphQL API is more flexible than REST due to the way it handles data fetch requests.

REST often over-fetches or under-fetches data if the data is of a slightly different type than what’s commonly requested. GraphQL API allows clients to request exactly the data they need, over-fetching and under-fetching of data. Unlike REST, which may have multiple endpoints, GraphQL uses a single endpoint to handle all requests.

An example GraphQL query and response will look something like the following:

2. gRPC#

gRPC is an open-source framework developed by Google that enables efficient, lightweight communication between distributed systems and services. It’s based on the Remote Procedure Call (RPC) model. It uses Protocol Buffers (protobuf) for defining data structures and communication contracts, enabling smaller and faster serialized messages compared to JSON or XML. gRPC APIs follow a Remote Procedure Call (RPC) model, where a client can directly invoke methods on a server as if they were local over various transports like HTTP/2.

While REST APIs are popular, other types like GraphQL and gRPC exist. Each has unique strengths—GraphQL for flexibility, gRPC for speed, and so on—but REST remains a go-to for general-purpose applications.

Here is a table that compares REST, GraphQL, and gRPC for your quick reference:

Next steps for your learning#

If you’re just starting out, this blog on REST APIs should give you some context on the popularity of this powerful system. While a great tool for you, it’s important to keep your mind open to other API types so you can recognize when a situation calls for a non-REST solution. Back-end development is a common example of when pure functional or another type of HTTP service is more useful than RESTful HTTP.

Consistent practice and exploring real-world applications will solidify your understanding and help you grow in the field. You can explore the following projects for hands-on practice with APIs:

• Create a REST API with FastAPI for User Management

• Integrate GraphQL to the Ruby on Rails Application

• Build a REST API with Elixir and Phoenix