Application Programming Interfaces, or APIs, are a way for computer programs or services to communicate with each other. This communication usually happens over an API endpoint, exposed by a program that a client consumes.

This article will compare two popular approaches to building APIs: representational state transfer (REST) API and Web API.

What Is a REST API?

Contrary to popular belief, REST API isn’t a protocol. It’s an architecture, and it’s the most popular architecture for developing APIs. As we explain in GraphQL vs REST: Everything You Need To Know, REST is stateless, so no data or status is stored between requests.

REST also defines multiple architectural constraints for building applications that communicate over HTTP:

  • Client-server architecture
  • Statelessness
  • Uniform interface
  • Cacheability
  • Layered system architecture
  • Code on demand

REST is easier to use than other API protocols or architectures. It also offers numerous other benefits that make it the first choice for many developers building APIs:

  • Diverse message formats: REST APIs are mostly used with JSON for serializing data but work with several message formats, including JSON, HTTP, plain text, and XML. This array of options gives it an edge over protocols like Service Object Access Protocol (SOAP) that primarily work with XML over HTTP, with options like JSON being significantly lighter, more flexible with support for arrays, and easier to parse compared to XML.
  • HTTP methods: REST is typically used with any of the GET, POST, PATCH, DELETE, or PUT methods for data retrieval and making requests depending on the service implementation. These methods return common HTTP success and failure codes. Other methods include OPTIONS, HEAD, and TRACE. These methods are inconsistent among services as some providers may only implement a single method according to their needs.
  • Decoupled architecture: REST has a client-server architecture, so its logic is separated from presentation — multiple parts can be simultaneously worked on without interference.
  • Scalability: REST APIs are simple, which makes them straightforward to use. However, if you need to scale up, you can create new endpoints to incorporate more complex logic.
  • Cacheability: While REST is stateless, the server response on the client can be cached to avoid repeating redundant requests. The server response usually gives information on how caching should be executed — with the client caching requests for a given period.
  • Security: In most cases, REST endpoints are exposed via HTTPS endpoints, which ensures that all API communication is secured using TLS/SSL. REST also supports other authorization and authentication schemes, like OAuth2 and JSON Web Tokens (JWT).

What Is a Web API?

A Web API is simply an interface to access server resources over HTTP. The term refers to the concept rather than any specific technology — a Web API can be built with various technologies, like Java and ASP.NET. Web APIs use an open-source interface and leverage many client entities like browsers, smartphones, tablets, and laptops.

Web APIs implement protocol specifications with concepts like caching, versioning, and diverse content formats. A Web API may or may not be a REST API, depending on how it’s built. Web APIs are usually used on a distributed system to provide services on different devices, such as smartphones and laptops, and are limited to the web application’s client side.

Here are two examples of widely-used Web APIs:

  • Google APIs: These include YouTube APIs, which allow developers to embed YouTube videos into their applications such as websites, and Google Maps API, which allows developers to use or embed Google Maps on webpages using JavaScript or Flash interfaces.
  • Twitter APIs: These include the Twitter search API, which provides methods to interact with Twitter search, and the REST API, which allows you to access core Twitter data.

A Web API is carried out as a system-to-system interaction. Here’s how the data within such an API might flow:

  1. The client device sends requests to the web server.
  2. The web server receives the request, processes it, then sends it back to the client device to be executed.
  3. The output is rendered to the user.

The beneficial features of Web APIs include:

  • Lightweight architecture: Web APIs excel in devices with limited bandwidth, such as smartphones.
  • Descriptive message headers: Web APIs have descriptive message headers, which may contain information on the content type, security scheme, or how to handle caching.
  • Supports all data types: The body of a web API can be used for anything, including binary files (videos, images, documents), plain XML, JSON, and HTML.
  • Resource-oriented service: A web API can expose resources in a way that conforms to the REST architecture.
  • Easy configuration and setup: Web APIs are easy to set up and run.

Web API vs REST API

Now, let’s compare these two APIs in more detail.

Architecture Similarities

Web and REST APIs share some architectural similarities — let’s take a look at them.

  • Statelessness: HTTP requests happen in isolation and are fundamentally stateless, as each request contains enough information to complete it. Multiple requests are only associated with each other through shared information, such as cookies or a session ID. The absence of state synchronization reduces the complexity and increases performance as the server doesn’t need to keep track of client requests. Concurrent requests can also be scaled across multiple servers.
  • Layered architecture: They both support a layered architecture design where API deployment, request authentication, and storage could happen across multiple servers.
  • Resource-oriented: In resource-oriented architectures, resources are mapped to Uniform Resource Identifiers (URIs). Both Web and REST APIs are resource-oriented as they expose resources via URIs.
  • Cacheability: In REST and Web APIs, queries that return the same information every time they’re called are cached. For example, an OPTION call on an endpoint will be cached as the output is the same regardless of how many times it’s called. This property, known as idempotence, is a good basis for determining when data can be cached. Idempotence is always considered in REST, although not nearly as much in web APIs. An idempotent API call is one where results will never change — no matter how many times it’s called — even with the possibility of something changing on the server. Examples of idempotent methods include GET, HEAD, and OPTIONS.

Architecture Differences

While Web APIs and REST APIs have similar architectural patterns, they also have some key differences.

  • Client and server-side coordination: REST APIs have loosely coupled architecture, allowing for independent development on the client and server side. With Web APIs, changes between client and server are more finely coordinated.
  • Interface: Depending on implementation details, REST APIs tend to use industry-standard interfaces. Web APIs use custom interfaces, depending on the API provider.

Communication

Web APIs are flexible enough to leverage any communication style, while REST APIs are primarily used with JSON, XML, and plaintext. These options mean that REST APIs perform well for textual data transmission, such as create, read, update, and delete (CRUD) operations against a database, but are more restrictive when it comes to binary data.

Web APIs offer a much better experience for services requiring binary data — like music or video streaming services — as they support more message formats.

Use Cases

While these API formats are interchangeable in many cases, there are a few scenarios where one is better than the other:

  • Cloud services and applications: Due to their stateless nature, REST APIs are used in cloud services as stateless components can scale and redeploy to accommodate changes. Cloud services and metrics are usually best exposed as REST APIs as there is little need for custom code.
  • Streaming services: Web APIs have better support and low overhead of application binary data on memory or bandwidth-constrained devices, so they’re best for services that require streaming.
  • Database manipulation (CRUD): It’s simpler and easier to expose CRUD functionality over a REST API than a Web API.

REST APIs are difficult to manage for complex requests that need to access resources that are not arranged in a simple hierarchy. This is because of its URIs referencing resources, meaning managing this kind of situation involves manipulating URI paths, query parameters, and the request body, which defeats the purpose of REST. In this case, a web API is preferred because it allows customization and has extensive support for URI response and request headers.

With support for techniques like asynchronous calls — which are not easily implemented using the REST architecture — web APIs are the way to go for complex API needs.

Summary

Web and REST APIs are used to build applications that provide resources and communicate over HTTP. While REST describes architectural constraints over a uniform interface, web APIs are generally a concept that can be RESTful, depending on implementation.

Both Web and REST APIs are lightweight formats that are interchangeable in many situations. However, compared to REST APIs, Web APIs provide a more customized experience and support for more message types, and it supports complex interactions between servers and clients dealing with binary data.

And with Kinsta’s application hosting services, you can build, test, and ship your API projects to the cloud faster and more efficiently.

Salman Ravoof

Salman Ravoof is a self-taught web developer, writer, creator, and a huge admirer of Free and Open Source Software (FOSS). Besides tech, he's excited by science, philosophy, photography, arts, cats, and food. Learn more about him on his website, and connect with Salman on Twitter.