This tutorial shows how to call a web API from a .NET application, using [System.Net.Http.HttpClient.](https://msdn.microsoft.com/library/system.net.http.httpclient(v=vs.110).aspx)
To learn how to implement this API with ASP.NET Web API, see [Creating a Web API that Supports CRUD Operations](xref:web-api/overview/getting-started-with-aspnet-web-api/tutorial-your-first-web-api
For simplicity, the client application in this tutorial is a Windows console application. **HttpClient** is also supported for Windows Phone and Windows Store apps. For more information, see [Writing Web API Client Code for Multiple Platforms Using Portable Libraries](https://blogs.msdn.com/b/webdev/archive/2013/07/19/writing-web-api-client-code-for-multiple-platforms-using-portable-libraries.aspx)
`RunAsync` runs and blocks until it completes. Most **HttpClient** methods are async, because they perform network I/O. All of the async tasks are done inside `RunAsync`. Normally an app doesn't block the main thread, but this app doesn't allow any interaction.
From the **Tools** menu, select **NuGet Package Manager** > **Package Manager Console**. In the Package Manager Console (PMC), type the following command:
This class matches the data model used by the web API. An app can use **HttpClient** to read a `Product` instance from an HTTP response. The app doesn't have to write any deserialization code.
**HttpClient** is intended to be instantiated once and reused throughout the life of an application. The following conditions can result in **SocketException** errors:
* Sets the base URI for HTTP requests. Change the port number to the port used in the server app. The app won't work unless port for the server app is used.
* Sets the Accept header to "application/json". Setting this header tells the server to send data in JSON format.
The **GetAsync** method sends the HTTP GET request. When the method completes, it returns an **HttpResponseMessage** that contains the HTTP response. If the status code in the response is a success code, the response body contains the JSON representation of a product. Call **ReadAsAsync** to deserialize the JSON payload to a `Product` instance. The **ReadAsAsync** method is asynchronous because the response body can be arbitrarily large.
**HttpClient** does not throw an exception when the HTTP response contains an error code. Instead, the **IsSuccessStatusCode** property is **false** if the status is an error code. If you prefer to treat HTTP error codes as exceptions, call [HttpResponseMessage.EnsureSuccessStatusCode](https://msdn.microsoft.com/library/system.net.http.httpresponsemessage.ensuresuccessstatuscode(v=vs.110).aspx) on the response object. `EnsureSuccessStatusCode` throws an exception if the status code falls outside the range 200–299. Note that **HttpClient** can throw exceptions for other reasons — for example, if the request times out.
When **ReadAsAsync** is called with no parameters, it uses a default set of *media formatters* to read the response body. The default formatters support JSON, XML, and Form-url-encoded data.
Instead of using the default formatters, you can provide a list of formatters to the **ReadAsAsync** method. Using a a list of formatters is useful if you have a custom media-type formatter:
1. [Download](https://github.com/aspnet/Docs/tree/master/aspnet/web-api/overview/advanced/calling-a-web-api-from-a-net-client/sample/server) and run the server app. [Download instructions](https://docs.microsoft.com/aspnet/core/tutorials/#how-to-download-a-sample). Verify the server app is working. For exaxmple, `http://localhost:64195/api/products` should return a list of products.
