what is the purpose of api in web development code example

Example 1: what is web api

// The ASP.NET Web API is an extensible framework for building HTTP based services.
// It works more or less the same way as ASP.NET MVC web application except that it sends data as a response instead of html view.

Example 2: purpose of api

Knowing the purpose of the API will
set a firm foundation for you to
well prepare your test data for input
and output. This step also helps you
define the verification approach.
For example, for some APIs, you will
verify the responses against the
database; and for some others, it is
better to verify the responses 
against other APIs.