I have heard of many web APIs like that of Facebook Twitter

I have heard of many web APIs like that of Facebook, Twitter, etc., which helps third party access data and manipulate it. I would like to know how a web API works. What are the basics of a web API?

If I want to create an API for my site, so that people can access or update it, what will I need to start with?

Solution

At its simplest, you create a set of GET/POST requests that anyone can call and publish the information on the URLs, parameters and effects. GET requests for read-only tasks and POST requests for anything that will change data on the server.

Add in a authentication system if needed and you have yourself a simple Web API.

A Web API is just an Interface to allow access to your system (such as site) via standard HTTP request methods. The data itself is usually wrapped in some standard format (such as JSON or XML) to make it easy to handle.