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Open API: The Future of Application Programming Interfaces

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Open APIs are improving accessibility and compatibility for developers' applications.

"Application Programming Interface," or API, as it is more commonly called, is probably one of the most used terms these days when it comes to software and application development. More often than not, one is likely to hear an announcement of new APIs from time to time. These largely pertain to applications, web browsers, and even operating systems. They are prolific and they are a lifeline for developers.

With the advent of the OpenAPI system, they have become even more popular and their uses in the industry are widespread. This is largely due to the fact that they are known to allow for better leverage in the scope of an application’s usage. Delving into this article, we shall but see what defines OpenAPI and its scope in the future.

What is the Difference Between API and OpenAPI?

APIs are what allow interaction between two sets of applications. This is defined by a set of specific rules that allow developers to access the core or certain features of an application. It can be compared to a user interface that allows the user to interact with a software application. So, each time you are using an application like Twitter, or accessing the day’s weather on our phone, you are using an API.

When you use an application on your phone, it connects over the Internet and sends data across to the server. The latter retrieves the data and sends it back to your phone, which then receives the data and presents it in a format that makes it useful and readable to you.

An open API is nothing but an API that has been made open to the public. Such an API can be accessed by third-party applications so developers can harness the features of the application as per their suitability. They are published on the Internet so that the owner of the API can make it accessible to consumers.

While public API and OpenAPI are often used interchangeably, they are different in terms of sharing and restrictiveness. Open APIs are freely shareable and mostly developed using open source technology. Public APIs are not entire shareable and are restricted in terms of sharing and largely done with keeping security aspects in mind. Hence, they may often use custom data formats and proprietary protocols.


OpenAPI is also very different from previous iterations of APIs, which had their own pros and cons. Private APIs were only accessible to a select few in a company or project and so, only the specific publisher of the API could administer changes to the API. While that made collaboration more straightforward, it also meant that it wasn’t really compatible with outside applications.

Timely updates were also an issue as development was dependent on only one group of developers. The seeming sole advantage was that back-end data wasn’t accessible to the outside world and so offered some form of security.

OpenAPI negates compatibility issues but at the same time, introduces the security issue. While the API is available to the public, it allows for better compatibility between applications and also faster, timely updates. But, management can get out of control and also, there is public access to back-end data.

What is OpenAPI Specification?

OpenAPI Specification, or OAS, is vendor neutral in nature and is meant to be a description format for APIs that are based on HTTP. The origins of it trace to SmartBear Software, who donated it in 2015 and was then based on the Swagger 2.0 specification.

Currently, it is maintained and promoted by the OpenAPI Initiative, which is under the Linux Foundation. Due to this, it maintains an open governance structure, meetings and decisions are made public, thus enabling anybody to propose and discuss anything to do with it.

Also, due to its open-nature structure, it has created a vast amount of tools that spell out the capability of open and machine-readable API description. These are called documents in OpenAPI terminology. The amount of tools that are available to developers when working with OpenAPI ensures its popularity and wide adoption in the industry.

Another point to note is that, while OAS describes APIs based on HTTP (REST), it is also applicable for HTTP-like protocols, such as the CoAP (Constrained Application Protocol). Hence, it can be used in cases that have restricted resources as well.

OpenAPI – Best Practices

There are certain practices, which although not tied to OpenAPI specifications, ensure the creation of OpenAPI documents in a simple and easy manner. Some of these are discussed below.

  • Using a Design-first approach

Writing API description happens via two methods, code-first or design-first. However, the latter works out to be the best approach as the number of APIs that can be created in code is superior to what can be used to describe using OpenAPI.

  • Single source of information

No matter what your design approach may be, it is advisable to keep only one source of information and not duplicate it. This is a very basic practice to follow. If using multiple sources, information updated in one place may not be updated in other places, leading to grave issues.

  • Addition of OpenAPI documents to Source Control

OpenAPI documents are first-class source files and hence, they may be used in several automated processes such as unit testing and documentation rendering. In fact, they should be the first files to be committed to source control.

  • Making OpenAPI Documents available to users

Documents that are rendered well can be very useful to users of an API, but often they may need to access the source OpenAPI description. Thus, making these documents available to users can be a good option.

  • Avoid writing OpenAPI Documents by hand

While it may be tempting to write OpenAPI documents by hand, as they are simple and in plaintext, they can turn out to be highly impractical in large projects. Hence, the use of OpenAPI Editors, Domain-Specific Languages, or Annotations, can certainly help.

Open API & Machine-Readable API Descriptions

API descriptions that are machine readable are not a new thing. In fact, local APIs have long existed. Take the example of method signatures in C or the use of method definitions in C# and Java.

When the Internet surfaced, remote APIs surfaced as well. However, problems that were faced during the use of assembly language too, started to resurface, specifically when requests were made in an unexpected format to the server.

Machine-readable API descriptions were brought about to bring the same amount of vigorousness that were brought by method signatures to local APIs. Currently, there are tools that can check if requests are made in the correct format and even take the onus for them. At present, machine readable API descriptions have been able to surpass method signatures, on the benefits front.

Implementations of OpenAPI

The works of OpenAPIs are manifold and vary across the sectors they are being used in. For example, in the business sector, we have seen OpenAPI being used in the development of innovative and better applications. Due to its open nature, it can be changed and developed to suit the need of businesses.

In the web sector, OpenAPI is being used for the interchange of information from one website to another by sending HTTP requests, to which the other website responds. YouTube is one of the best examples in this arrangement.

To aid in the integration of APIs with external applications, API providers also make use of proper documentation.

Features of OpenAPI

With OpenAPI gaining popularity each day, here are some of the main features that it offers.

  • Free usage

OpenAPI may be used by any developer, whether they are from the organization that published it in the first place or not. This helps for better compatibility and offers flexibility in development.

  • Integration

OpenAPI can be integrated with back-end data, which aids developers in bettering the performance of their applications. However, this access to back-end data can also be restricted to the public by the publisher. However, the data that is provided does not require any copyright.

  • Support for Open Standards

OpenAPIs are based on open standards and hence can be beneficial to those developers and organizations that want to harness its features without spending much capital.

Advantages of OpenAPI

OpenAPI has grown in importance owing to the fact that it offers many advantages. Some of these are –

  • Description Validation: It allows for a check-in terms of the correctness of the description file syntactically. It also ensures adherence to a specific version of the Specification and so that it is in line with the formatting guidelines set by the team.

  • Data Validation: The data that is flowing through the API (bilaterally) is checked for correctness, both during the development process and on deployment.

  • Documentation: Creation of documentation on the basis of machine-readable description. This is always kept up-to-date.

  • Generation of Code: By creating both the server and client code in any programming language, it helps free developers from the additional task of performing data validation or writing glue code for SDK.

  • Graphical Editors: With graphical editors, creation of description files using a GUI ensures easiness and comfort.

  • The use of Mock Servers: Mock servers can be created and they help in providing example responses for the start of the testing process.

  • Security: One can discover the possible vulnerabilities at the API design stage.

Besides these, OpenAPI also means that you are choosing a non-proprietary format, on which you have a future say. On the downside though, it is worth remembering that if the publisher of the API decides at a later point to charge a licensing fee or change the terms, the third parties who have used it have little recourse other than to go along with it.

Tech Target also points out the importance of treating an Open API as you would other customer-facing software, ensuring it is free from bugs and security leaks and ensuring it doesn't impede performance.

Modern Application Development with OpenAPI

Since their foundations, APIs have come a long way. They are the mainstay for application development and work as an intermediary between several applications and websites.

However, OpenAPIs seem to have clearly taken over as the mainstay these days. And considering the advantages offered by it, they are even being touted as the next generation of open-source software. The cross compatibility offered by the use of OpenAPIs only make its significance greater in today’s connected world. It offers better connectivity between applications and websites, also giving better control to developers.


As the world keeps growing and more devices require interaction on a better level, the usage of Open APIs can only get bigger. They are open, free to use and also easier to implement. Despite the fact that back-end data access can cause some security issues, the benefits provided by it are manifold. Therefore, it is safe to say that OpenAPI has a bright future.


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Kaushik Pal
Technology writer
Kaushik Pal
Technology writer

Kaushik is a technical architect and software consultant with over 23 years of experience in software analysis, development, architecture, design, testing and training. He has an interest in new technologies and areas of innovation. He focuses on web architecture, web technologies, Java/J2EE, open source software, WebRTC, big data and semantic technologies. He has demonstrated expertise in requirements analysis, architectural design and implementation, technical use cases and software development. His experience has covered various industries such as insurance, banking, airlines, shipping, document management and product development, etc. He has worked on a wide range of technologies ranging from large scale (IBM…