Web API

What is Web API?
Web API is a new web application runtime that builds on the lessons and patterns proven in ASP.NET MVC. Using a simple controller paradigm, Web API enables a developer to create simple HTTP web services with very little code and configuration. WebAPI is an ideal platform for building pure HTTP based services where the request and response happens with HTTP protocol. The client can make a GET, PUT, POST, and DELETE request and get the WebAPI response appropriately.
ASP.NET Web API is a framework that makes it easy to build HTTP services that reach a broad range of clients, including browsers and mobile devices. ASP.NET Web API is an ideal platform for building RESTful applications on the .NET Framework.

WebAPI is

• An HTTP Service
• Designed for broad reach
• Uses HTTP as an Application protocol, not a transport protocol

Why Web API?
Today, a web-based application is not enough to reach it's customers. People are very smart, they are using iphone, mobile, tablets etc. devices in its daily life. These devices also have a lot of apps for making the life easy. Actually, we are moving from the web towards apps world.
Web API is the great framework for exposing your data and service to different-different devices. Moreover Web API is open source an ideal platform for building REST-ful services over the .NET Framework. Unlike WCF Rest service, it use the full featues of HTTP (like URIs, request/response headers, caching, versioning, various content formats) and you don't need to define any extra config settings for different devices unlike WCF Rest service.

How Web API is different from WCF

WCF	ASP.NET Web API
Enables building services that support multiple transport protocols (HTTP, TCP, UDP, and custom transports) and allows switching between them.	HTTP only. First-class programming model for HTTP. More suitable for access from various browsers, mobile devices etc enabling wide reach.
Enables building services that support multiple encodings (Text, MTOM, and Binary) of the same message type and allows switching between them.	Enables building Web APIs that support wide variety of media types including XML, JSON etc.
Supports building services with WS-* standards like Reliable Messaging, Transactions, Message Security.	Uses basic protocol and formats such as HTTP, WebSockets, SSL, JQuery, JSON, and XML. There is no support for higher level protocols such as Reliable Messaging or Transactions.
Supports Request-Reply, One Way, and Duplex message exchange patterns.	HTTP is request/response but additional patterns can be supported through SignalRand WebSockets integration.
WCF SOAP services can be described in WSDL allowing automated tools to generate client proxies even for services with complex schemas.	There is a variety of ways to describe a Web API ranging from auto-generated HTML help page describing snippets to structured metadata for OData integrated APIs.
Ships with the .NET framework.	Ships with .NET framework but is open-source and is also available out-of-band as independent download.

Web API Features

• It supports convention-based CRUD Actions since it works with HTTP verbs GET, POST, PUT and DELETE.
• Responses have an Accept header and HTTP status code.
• Responses are formatted by Web API’s MediaTypeFormatter into JSON, XML or whatever format you want to add as a MediaTypeFormatter.
• It may accepts and generates the content which may not be object oriented like images, PDF files etc.
• It has automatic support for OData. Hence by placing the new [Queryable] attribute on a controller method that returns IQueryable, clients can use the method for OData query composition.
• It can be hosted with in the applicaion or on IIS.
• It also supports the MVC features such as routing, controllers, action results, filter, model binders, IOC container or dependency injection that makes it more simple and robust.