What Is ASyncAPI and How Does It Differ from OpenAPI?

Those who work in the API industry have likely seen the evolution of two big names in defining API interfaces: OpenAPI and AsyncAPI.

The OpenAPI Specification, originally known as the Swagger Specification, was launched in 2010 during a new heyday for API development. Its contemporary, the AsyncAPI Specification, was released seven years later in 2017.

To date, both are under the governance of open-source initiatives and have made quite the impact on API design, particularly for areas like API documentation. But what are the qualities that set the two formats apart? And when it comes down to it, which format should you choose for the design of your own API?

Here’s a rundown of two of the most helpful tools in API design. Learning about the best applications for OpenAPI and AsyncAPI can further your mastery with the latest API tools, like the Stoplight OpenAPI visual editor.

AsyncAPI, OpenAPI, and the Best Choice for an API Specification

Before you compare OpenAPI and AsyncAPI, however, it’s important to know what exactly you’re achieving when you adopt a description format. The API description format serves as a framework for defining the product’s interface, which can make the entire design process more organized and consistent. Some factors that you should be considering are the following:

  • Whether the format used for describing is human-readable or machine-readable.
  • What kind of API design architecture the format is meant to clarify.
  • The role the description format will play in tasks like API code generation and documentation.
  • How easy it will be for API developers to work with the format.
  • How integrable and adaptable the format will make the final API product to its potential adopters.

Both OpenAPI and AsyncAPI are machine-readable specification formats. They also share a common history, as one’s creation was inspired by another’s. But there are big differences in terms of what kind of API they’re best used for. What follows below is a brief summary on both OpenAPI and AsyncAPI.

OpenAPI: A Briefer on the “Industry Standard” for REST APIs

The first iteration of the OpenAPI Specification, called Swagger, had its beginnings as part of the online dictionary service Wordnik. The Swagger Specification’s progenitor was Tony Tam. Tam’s creation was eventually acquired by SmartBear Software and later donated to the OpenAPI Initiative.

OpenAPI Specification is an open-source solution that’s widely used to describe REST APIs, or APIs that follow the Representational State Transfer architectural design. OpenAPI is praised among REST API designers for the following:

  • It has a language-agnostic quality, which means it can work with different programming languages with minimal instruction.
  • It affords a high level of standardization for design-related tasks, such as compiling endpoints.
  • It can smoothly sync up the API’s source code, libraries, and executables for tasks like API documentation.
  • It has great appeal to the larger REST API design community, as many are already familiar with how to use it.
  • It’s backed by significant mindshare in the API industry, who consistently contribute to the improvement of OpenAPI technology.

Much of the OpenAPI Specification’s attractiveness lies in how easy, streamlined, and accessible it makes REST API design. These values actually inspired the creation of OpenAPI’s contemporary, AsyncAPI.

AsyncAPI: New Innovations for Message-Driven Microservices

The AsyncAPI Specification aspires to be like what OpenAPI Specification is for REST APIs—that is, the industry standard, but for the asynchronous message-driven API. Just like OpenAPI, AsyncAPI is governed by its own open-source initiative. Its creator, Fran Mendez, is currently the AsyncAPI Initiative’s project director.

AsyncAPI Specification is a method that lends itself well to the design of message-driven APIs, where the API publisher knows its intended recipients. It began as a way to accommodate message-driven API architecture just as easily as OpenAPI did for REST APIs. In the process, AsyncAPI filled in some important gaps:

  • It’s a specification that allows API stakeholders to define interfaces for asynchronous APIs in particular.
  • It’s responsive to message-driven API architecture, whose principles rely on asynchronous and non-blocking messages.
  • It contributes to a better tooling ecosystem for message-driven APIs.
  • It chronicles important aspects of message-driven API design, such as the message format and consequent updates to code.
  • It standardizes communication within the message-driven API system.

Message-driven APIs are built along a very different rationale than REST APIs. This type of API relies on a reactive system, propped up by the accommodation of asynchronous messages. Simply put, AsyncAPI Specification is the description format specially built for message-driven APIs. It’s meant to be as snug a fit for message-driven APIs as OpenAPI Specification is for REST APIs.

Should You Choose ASyncAPI or OpenAPI for Your Project?

Suffice to say, neither specification will serve as the “all-in-one” tool for describing APIs.One of these protocols may suit your design process better than the other. You can push for the adoption of OpenAPI for RESTful, HTTP-driven services. If you’re describing a message-driven service, however—for example, an API that oversees asynchronous order processing on an ecommerce store—choose AsyncAPI.

Once your format fits the type of API you’re looking to build, your design process will be that much more streamlined. You’ll also be able to choose the best tooling systems to fit the format and kick off your API design in earnest. Whether you’re spearheading a REST API or a message-driven API, here’s to your success in launching your product to the market!

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