programming interfaces represents an important part of software architecture, the organization of a complex piece of software. The principle of information hiding describes the role of programming interfaces as enabling modular programming by hiding the implementation details of the modules so that users of modules need not understand the complexities inside the modules. Aside from the previous underlying principle, other metrics for measuring the usability of an API may include properties such as functional efficiency, overall correctness, and learnability for novices. One straightforward and commonly adopted way of designing APIs is to follow Nielsen's heuristic evaluation guidelines. The Factory method pattern is also typical in designing APIs due to their reusable nature. Thus, the design of an API attempts to provide only the tools a user would expect. Synchronous versus asynchronous An application programming interface can be synchronous or asynchronous. A synchronous API call is a design pattern where the call site is blocked while waiting for the called code to finish. With a asynchronous API call, however, the call site is not blocked while waiting for the called code to finish, and instead the calling thread is notified when the reply arrives. Security API security is very critical when developing a public facing API. Common threats include SQL injection, Denial-of-service attack (DoS), broken authentication, and exposing sensitive data. Without ensuring proper security practices bad actors can get access to information they should not have or even gain privileges to make changes to your server. Some common security practices include proper connection security using HTTPS, content security to mitigate data injection attacks, and requiring an API key to use your service. Many public facing API services require you to use an assigned API key, and will refuse to serve data without sending the key with your request. Release policies APIs are one of the more common ways technology companies integrate. Those that provide and use APIs are considered as being members of a business ecosystem. The main policies for releasing an API are: Private: The API is for internal company use only. Partner: Only specific business partners can use the API. For example, vehicle for hire companies such as Uber and Lyft allow approved third-party developers to directly order rides from within their apps. This allows the companies to exercise quality control by curating which apps have access to the API and provides them with an additional revenue stream. Public: