What is an API spec?

Wed Oct 13 2021

2 min read

There are a lot of APIs out there, each with different specifications. The developers define these specifications when building an API to set some standards right from the start. Let’s take a look at some of these specifications.

API Specs

It is used to standardize data exchange between web services. Standardize means the ability of diverse systems, written in different programming languages, to run on different operating systems, or use various technologies to communicate.

The API specification provides a comprehensive understanding of how an API behaves and links with other APIs. It also explains how the API functions and the results to expect when using the API.

There are four types of API specifications:

  • Representational State Transfer (REST)
  • Simple Object Access Protocol (SOAP)
  • GraphQL
  • Remote Procedure Call (RPC)


REST API is one of the most common specifications of API. REST APIs allow you to perform CRUD (create, read, update, and delete) operations between a client and a server. It connects your backend with your frontend so they can communicate with each other.


SOAP API is another type of web service that allows communication between client and server. Any web service that complies with the SOAP web services specification is a SOAP web service. The W3C (World Wide Web Consortium) is behind these specifications.


The GraphQL API is designed to provide you with the precise amount of data you request. With the REST API, you often encounter the problem of over-fetching and under-fetching, and GraphQL solves these problems.


It is a simple interaction where a local client sends commands to a remote server. Both client and server use different call parameters, and these parameters are converted on both sides. These conversions happen through stubs that are dedicated pieces of code responsible for transforming and deconverting the call function parameters.