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RESTful Web API Design – A Comprehensive Guide

RESTful web API design

Web APIs are pretty common these days. From Google SERP scarping and IP geolocation to number verification and exchange rates data, developers worldwide are creating different web APIs for various purposes. Even tech giants like Amazon, Google, Facebook and Twitter offer various APIs for web development projects. Even though APIs are designed to ease the web development process, they can cause severe problems if not designed properly. When it comes to API design, developers either use REST or SOAP design models. While both approaches have their advantages, REST has become the dominant design model due to its simplicity, easy integration, support for various formats, and ease of use and learning.

This detailed guide will cover the basic concept of RESTful APIs, their working and all the key aspects of designing a REST web, including best practices. We’ll also explore some of the best RESTful APIs by APILayer.


API Design - what is an API

First, let’s define an API.

An API (Application Programming Interface) allows two software programs or applications to communicate, interact or talk to each other. It basically acts as a middleman or intermediary between two apps, allowing them to exchange data. A REST API is an API built using the REST design model.

REST refers to REpresentational State Transfer. Unlike SOAP, which is a protocol, REST is an architectural style that allows us to create web services, such as API, independent of programming languages. Moreover, REST supports various data formats, such as JSON, CSV, and XML, whereas SOAP only supports

In a RESTful API, we can make requests using a simple URL. Moreover, a unique URL identifies only a single resource. These APIs support various HTTP methods to perform tasks. These include GET, POST, PUT or DELETE. Some APIs also support additional HTTP methods, such as COPY, LINK, UNLINK, and PATCH, but these are very common.

Features of REST

Independent code implementation: Using the REST design model, developers can implement server-side and client-side code independently. As a result, developers can easily make changes on the client side whenever needed without affecting the server side and vice versa. This decoupling also makes it easy to scale the product as required.

Stateless: REST-based APIs can be designed to be stateless, simplifying the server-side design and improving the API’s overall performance. In stateless API operations, servers aren’t responsible for maintaining any client state.

Resource caching: The client can create a mechanism for cache responses based on the received data.

Layered system: Using REST, developers can design several hierarchical layers to restrict components from interacting beyond their interaction layer.

Code on demand: In REST APIs, servers typically return data in JSON or XML format. However, they can also respond with executable code when needed, enhancing client-side functionality.

How To Design A REST API and What Are The Best Practices for API Design?


Before you start designing an API, deciding how the API will expose data/functionality to the API users is essential. Here are the key steps for RESTful API design and API design best practices:

Simple URL Structure

It’s essential to keep the base URL of your API simple and easy to read. This makes the API easy to use for API consumers and results in easy adoption on platforms that don’t have a properly-support client library.

Here is an example of a good base URL:

Moreover, if you’re designing an API that provides real-time exchange rates, a good URL could be:

Naming Best Practices

Using a standardized format or common patterns for naming makes it easy for API users to discover functionality and guess names and meanings of common properties without referring to the API documentation constantly.

Here are some of the best naming practices:

1) Always use nouns in API URLs for resources instead of verbs. We have HTTP methods to describe different functions of REST APIs, so we don’t need verbs in naming the resources. For example, if you’re developing a currency rate API, you could use ‘lastest’ for real-time exchange rates instead of ‘getLatestRates.’

2) A good practice is to keep the resource name plural. Although it’s not a requirement, singular names can create confusion about whether we’re requesting a single resource or a list of resources. It’s also essential to keep the name of resources uniform across your API.

An example of a plural resource name is as follows:


Using a plural name (‘Wheels’) also eliminates the need to add all with the resource, such as /cars/{id}/wheels/all

3) It’s best to avoid using articles like ‘the’, ‘a’, ‘ and ‘of’ unless absolutely necessary.

4) Another best practice is using lowercase letters to name URI paths.

5) Avoid using file extensions in URIs. This will reduce the overall URI length and make the URI simple and visually appealing.

6) Sometimes, API producers need to define a way to allow users to get a specific resource or resources and improve the developer experience. For example, in an exchange rates API, you may want to enable users to get foreign exchange rates for a specific continent. In such a case, you can use parameters.


API versioning is a crucial part of API design and development. It basically involves creating different versions of an API for different purposes and use cases. Versioning enables API developers to update the API over time and ensures that existing projects aren’t affected by API changes. While developers use one API version in their existing projects, various API versions provide flexibility for future projects.

As an API developer, you can use a version as a query parameter or date. However, a good practice is to use it as a prefix to the resource, such as:


Use The Right HTTP Methods

REST APIs make use of various HTTP methods to perform different operations. And using the correct HTTP methods is crucial for a good API design. Typically, a REST API should support four basic HTTP methods corresponding to the CRUD operations:

GET: The GET HTTP method extracts data/resources specified in the API’s URI. The GET request only consists of a header. Here is an example GET API request:

POST: The POST method allows developers to create new resources on the server where the request is sent. In other words, this method is used for resource allocation. A POST client request consists of a header and a request body because it involves sending data. Below is a sample code for a POST request:

PUT: The PUT method enables developers to update an existing resource or create a new one. This method also involves sending data to the API, similar to POST.

DELETE: HTTP DELETE method is used to delete or remove a resource. 

Use the Right HTTP Status Codes

API Design - A person coding on laptop

When an API call or request is made, it is either successful or unsuccessful. In case of an unsuccessful response, API developers need to show the correct HTTP status code to the users, such as whether the request was successful, an error occurred, or any further action is required. These responses are crucial to the proper outcome and working of the API.

Here are the most common HTTP response or status codes:

  • 200: Operation/request was successful/ successful response

  • 201: New resource created successfully.

  • 204: Empty resource.

  • 400: Invalid request.

  • 401: Authentication is required.

  • 405: Invalid or incorrect HTTP method.

  • 415: Media/content type unsupported.

  • 429: Too many requests made by the user

  • 500-599: Server-side errors

Asynchronous operations

Sometimes an HTTP request, such as GET or POST requests, can require some time to process. In such a case, it’s best to make the operation asynchronous. For example, you can return the 202 HTTP status code, which means the request is accepted but is currently processing.

Data Limits and Pagination

Another crucial aspect of a good REST API design is using pagination and data limits. This is especially required for APIs that might return a large data set in response to a user request. If you don’t implement a mechanism for load balancing, the user can bring down the service. Using pagination and data limits, API developers can ensure not all requested data is sent in a single request.

Using pagination, API developers can split huge data into multiple smaller chunks or pages. With data limits, you can ensure that users only request and receive data within a certain limit. A good API design practice is to set a default data limit and offset.

Define Data Formats

Choosing the right request and response data formats is also essential to a good API design. A well-designed API uses JSON data format to return data. JSON is a lightweight modern-day data format that is human-readable and easy to parse. Additionally, the response body should include a descriptive message or error message and error codes if there is an error.

Implement User Authorization and Authentication Mechanisms

User authorization and authentication are crucial for data protection and security purposes and are essential for good API design. Authorization helps limit access permissions due to security concerns, whereas authentication helps ensure that only authenticated users can access the API and its data.

RESTful APIs typically make use of an API key to authenticate and identify a user. However, API producers must also implement advanced authorization and authentication techniques like the OAuth protocol. You should also focus on access control, validations, HTTP headers, and session management.

Detailed API Documentation

Many developers don’t focus on API documentation. However, extensive API documentation is essential for good API design. Good documentation includes all the details about API endpoints, methods, parameters, functionality, and responses. Additionally, it should include coding examples in various programming languages to ease the process of API integration. Here is an example of good API documentation.

Where Can You Find The Best REST APIs?

APILayer API marketplace for selling and finding a wide range of REST APIs

APILayer Marketplace offers a wide range of high-performance REST APIs, including finance, geo, communication, weather and currency APIs. All the REST APIs come with a free plan and have extensive documentation to help you get started quickly. Moreover, these high-performance APIs are highly scalable.


There are two main API design models, SOAP and REST, that use different data formats and communication protocols. However, most API developers today use REST, which offers several benefits over SOAP. For instance, REST supports various data formats, such as JSON, CSV, and XML, whereas SOAP supports only XML. This detailed guide includes key steps to designing high-performance REST APIs and best practices.

Sign up for APILayer today and use your desired REST API for free!

Frequently Asked Questions (FAQs)

What is API contract testing?

API contracts testing involves testing the format and content of API responses and requests.

What does API first design mean?

A first design means a well-designed API that enhances the developer experience and provides value to the business.

How do we design an API?

Designing an API involves creating an API base URL and URI, naming API resources and properties, creating API endpoints, using the correct HTTP methods and response codes, creating API documentation, and more.

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