Developers can access an open API, which is also known as a public API when the API is made available to the public. By publishing and freely disseminating Open APIs online, the owner of service accessible via the internet can provide that service to users anywhere in the world.

While there is no single best approach to creating an open API, making it accessible and easy to use by as many clients as possible should be a top focus. To that end, it is preferable to build open APIs with open source software and community-driven standards rather than with proprietary protocols or bespoke data formats.

Whereas the phrases "open" and "public" application programming interfaces (APIs) are sometimes used interchangeably, there are those who point out a key distinction: open APIs are freely available while public APIs are often more limited in what assets can be shared. This is because the proprietary company provides public access to its API and back-end data while desiring to exercise tight control over the application. Or, the corporation might offer a set of application programming interfaces (APIs) to inspire third-party developers in specific verticals to find and share innovative uses for the company's software product.

Why managing Open API is a challenge?
Once an API has been released to the public, it becomes difficult for a company to regulate who uses it and how. Because of the importance of keeping customers happy, API management must be treated carefully.

For example, organizations must be careful when they decommission older APIs, change the syntax of a RESTful method call, alter the structure of an XML or JSON payload, or retire a given piece of functionality as the control that might exist within an organization over how an API is used and who is using it does not apply to the public at large.

When updates to an API aren't handled well, consumers get frustrated, which might reflect poorly on the company offering the API to the public.

Advantages of Open APIs
The API publisher and the developers who access the API through an open format enjoy advantages.

Ability to reach more people without spending money on specialized software for doing so;  an opportunity to diversify income by licencing additional software; and The choice to keep one's company's source code in-house. Less reliance on third-party libraries and frameworks by development teams; Spending less time correcting coding errors; and The availability of one's favourite development tools without sacrificing access to an open API.

Twitter's success shows both the advantages and the pitfalls of open APIs.

In its early stages, Twitter only offered a primary web interface and a text-based format. After that, however, Twitter made an open API available that allowed programmatic access to its infrastructure.

As a result of the popularity of this API, a plethora of supporting applications and augmentations to its functionality emerged rapidly. For example, the popularity of Twitter photo-sharing increased after TwitPic was released. When Twitter's interface failed to impress users, they turned to more adaptable desktop clients like TweetDeck and Falcon Pro. A large part of Twitter's success story was due to the additional features and software applications that were developed using its open API.

However, some Twitter clients rejected or injected their ads, which negatively affected Twitter's business model. In addition, through acquisitions, API restrictions and trademark challenges, Twitter pushed back against some companies that used its open API.

Some members of the software development community felt betrayed by Twitter. They believed the community that developed apps using Twitter's open API played a large part in why Twitter became successful. Shutting down those APIs and filing trademark infringements against supporting services showed disregard for the many developers who played a role in Twitter's success, according to some in the developer community. However, Twitter executives said their actions sought to protect the company's trademarks, intellectual property, and the platform's security.