> For the complete documentation index, see [llms.txt](https://docs.futuregold.us/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.futuregold.us/ai-arbitrage-trade-system/5.-technical-details/5.2.-apis-of-cryptocurrency-exchanges/5.2.2.-apis-in-the-world-wide-web.md).

# 5.2.2. APIs in the World Wide Web

From a web development perspective, APIs are often a set of HTTP requests and the according HTTP responses, which are often encoded in the XML or JSON format. An alternative to HTTP-requests and -responses is the usage of WebSockets, which is an advanced technology that opens an interactive communication session between a server and a client and eliminates the need for polling the server permanently. 

Almost every large online service offers at least one API to developers, in order to make possible third-party applications that use functions or data from the original service. 

Examples for web APIs are:

• Facebook’s Graph API: It allows reading and writing Facebook user’s data, if the user authorizes the third-party app to do so. 

• YouTube Data API: Integrate YouTube features into an application, e.g. upload a video, manage a playlist, etc. 

• Google Maps API: A lot of things are possible with the API of Google Maps, e.g. putting a map on a website, finding information about places, getting directions and converting GPS coordinates into street addresses.