ASP.NET Web API is a framework for building and consuming HTTP services that can reach a broad range of clients including browsers, phones and tablets. You can use XML or JSON or something else with your API. JSON is nice for mobile apps with slow connections, for example. You can call an API from jQuery and better utilize the client’s machine and browser.
ASP.NET Web API includes support for the following features:
Modern HTTP programming model: Directly access and manipulate HTTP requests and responses in your Web APIs using a new, strongly typed HTTP object model. The same programming model and HTTP pipeline is symmetrically available on the client through the newHttpClient type.
Full support for routes: ASP.NET Web API supports the full set of route capabilities of ASP.NET Routing, including route parameters and constraints. Additionally, use simple conventions to map actions to HTTP methods.
Content negotiation: The client and server can work together to determine the right format for data being returned from a web API. ASP.NET Web API provides default support for XML, JSON, and Form URL-encoded formats and you can extend this support by adding your own formatters, or even replace the default content negotiation strategy.
Model binding and validation: Model binders provide an easy way to extract data from various parts of an HTTP request and convert those message parts into .NET objects which can be used by the Web API actions. Validation is also performed on action parameters based on data annotations.
Filters: ASP.NET Web API supports filters including well-known filters such as the [Authorize]attribute. You can author and plug in your own filters for actions, authorization and exception handling.
Query composition: Use the [Queryable] filter attribute on an action that returns IQueryable to enable support for querying your web API via the OData query conventions.
Improved testability: Rather than setting HTTP details in static context objects, web API actions work with instances of HttpRequestMessage and HttpResponseMessage. Create a unit test project along with your Web API project to get started quickly writing unit tests for your Web API functionality.
Code-based configuration: ASP.NET Web API configuration is accomplished solely through code, leaving your config files clean. Use the provide service locator pattern to configure extensibility points.
Improved support for Inversion of Control (IoC) containers: ASP.NET Web API provides great support for IoC containers through an improved dependency resolver abstraction
Self-host: Web APIs can be hosted in your own process in addition to IIS while still using the full power of routes and other features of Web API.
Create custom help and test pages: You now can easily build custom help and test pages for your web APIs by using the new IApiExplorer service to get a complete runtime description of your web APIs.
Monitoring and diagnostics: ASP.NET Web API now provides light weight tracing infrastructure that makes it easy to integrate with existing logging solutions such as System.Diagnostics, ETW and third party logging frameworks. You can enable tracing by providing an ITraceWriterimplementation and adding it to your web API configuration.
Link generation: Use the ASP.NET Web API UrlHelper to generate links to related resources in the same application.
Web API project template: Select the new Web API project form the New MVC 4 Project wizard to quickly get up and running with ASP.NET Web API.
Scaffolding: Use the Add Controller dialog to quickly scaffold a web API controller based on an Entity Framework based model type.