How OpenAPI Can Do More Than Simple Documentation

​In the parlance of API development, an API specification serves the purpose of standardizing data exchange between disparate web services. 

The specification offers developers and their stakeholders an important reference for how their API product is supposed to behave, as well as sync with other APIs.

In the olden days of the industry, the most widely used description formats were Web API Description Language (WADL) and Service Object Access Protocol (SOAP). But today, OpenAPI Specification, a description format governed by the OpenAPI Initiative, is considered the industry standard—especially for defining REST APIs.

It’s a pity, however, that OpenAPI Specification is primarily used as a tool for API documentation and nothing more. Granted, API documentation may be the most obvious type of application to use OpenAPI Specification for. Today’s sophisticated new API design toolkits can actually auto-generate documentation from prevailing OpenAPI definitions. This makes the essential task of API documentation faster, more efficient, and more accurate, all to the joy of API developers. But the wisest of the bunch will make the most out of OpenAPI Specification by utilizing it for other purposes in the API development lifecycle.
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Here are five important points on why OpenAPI for developers is a boon to the whole API project, and not just its documentation phase. If you’ve just started working with OpenAPI Specification, try it out with the following applications

OpenAPI Specification Can Serve as Basis for API Contracts

One important application of OpenAPI is its use in determining API contracts. These are formal agreements between API stakeholders about the scope and function of the end product. Before the actual design work on a REST API begins, the OpenAPI Specification can serve as a roadmap for all parties’ aspirations of the product. It can give concrete form to stakeholders’ expectations of the API’s behavior, desired endpoints, and accommodation of calls and responses.
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Thanks to the use of OpenAPI Specification in the API contract, developers and clients alike can get specific with what they want from the service. This is proof that using OpenAPI Specification early on in the API lifecycle—as early as the contract negotiation phase—is a good decision. 

OpenAPI Specification Can Guide Developers through a “Design-First”

OpenAPI Specification can also help developers draft a manifesto of sorts for their future design work. For many API developers, OpenAPI Specification serves as a keystone for a “design-first” approach. The “design-first” philosophy advocates agreeing upon the API’s endpoints, parameters, calls, and responses before a single line of code is written. A number of successful API projects credit the “design-first” ethos for consistent, carefully thought-out, and easily replicable design work. Thus, it’s good to think about OpenAPI Specification as more than a simple tool for documentation, but the driving force behind a “design-first” API strategy.

OpenAPI Specification Can Help You Mock API Components

Before you start writing your API documentation, you will probably spend some time mocking its components to see if they work as planned. Yet another practical application of OpenAPI Specification pertains to mocking. The fact that OpenAPI Specification can define schemas, otherwise known as ways that the API interacts with resources, counts for a lot. In the context of mocking, even before your API coding work starts in earnest, you already have material to create purposeful mocks. You can use the specification to generate mock servers or certain mock responses. It definitely beats creating mocks from scratch, and it will help you attain feedback for your API much faster.  

OpenAPI Specification Can Help You Conduct Purposeful API Testing

API tests are sometimes a pain point for developers, and for those who are new to testing, the work may seem overwhelming. You may not know where to begin testing, what to test, how long to keep testing, and what results you’re looking for. But the good news is, using OpenAPI Specification can streamline the testing phase of your API development as well. It’s possible to repurpose OpenAPI contracts to generate useful test cases that actually match with the API’s intended implementation. Doing so will save you the time of setting up API tests from scratch. And, more importantly, it will help you validate the request-response behaviors that are unique to your API. 

OpenAPI Specification Can Smoothly Integrate New SDKS into the API

​The last big benefit of OpenAPI Specification pertains to its role in scaffolding software development kits, or SDKs. SDKs are essentially virtual toolboxes containing code or other tools for building applications, and they allow developers to integrate with a variety of services. OpenAPI Specification can accommodate SDK stubs in a number of languages, for example Java and Scala. It will ultimately make it easier for you to onboard SDKs and further accelerate your API development, in much less time than without the specification. 

Conclusion: Greater Flexibility and Efficiency with OpenAPI

All in all, OpenAPI Specification can be used all throughout the API development lifecycle, and not just for post-development API documentation. It would be a shame to relegate the usage of OpenAPI Specification to docs and docs alone. Find more ways to utilize OpenAPI Specification, and you won’t regret the big difference that will make in your REST API design.