An open API is an application programming interface that is publicly available. Sometimes referred to as a public API, it is shared on the internet, giving developers the ability to access a proprietary software application or web service.
By contrast, a private API typically only opens parts of a business' backend data and application functionality to the use of developers and contractors who work for the business.
There are a few characteristics that open APIs typically share:
- There are few restrictions -- developers and others can use them as they see fit, although they might have to register with the service providing the API.
- Open data -- available to everyone to use however they like -- usually backs open APIs.
- They are based on an open standard.
With an open API, developers who work outside of a company can nonetheless access backend data from that company and use it to improve their own applications.
Open APIs have been described as a "win-win relationship." They can potentially create some security issues, but the payoff is that third-party developers can dream up innovative ways to use a company's software product -- ideas that might not occur to the company that created the software.
The goal of an open API is to let as many clients access the API as possible. For that reason, typically proprietary protocols or custom data formats are not used with open APIs. Instead, open-source technology and community-based standards are used.
Open APIs have been widely used in social media. For example, Facebook offers an open API that allows third-party tools to create photo albums or post to user news feeds.
Some software programs -- including Microsoft's SharePoint -- also have an open API component.