AspNetCore.Docs/aspnetcore/tutorials/dotnet-watch.md

---
title: Developing ASP.NET Core applications using dotnet watch
author: rick-anderson
ms.author: riande
manager: wpickett
ms.date: 10/14/2016
ms.topic: article
ms.assetid: 563ffb3f-d369-4aa5-bf0a-7300b4e7832c
ms.prod: aspnet-core
uid: tutorials/dotnet-watch
---
# Developing ASP.NET Core applications using dotnet watch

<a name=dotnet-watch></a>

By [Victor Hurdugaci](https://twitter.com/victorhurdugaci)

## Introduction

`dotnet watch` is a development time tool that runs a `dotnet` command when source files change. It can be used to compile, run tests, or publish when code changes.

In this tutorial we'll use an existing WebApi application that calculates the sum and product of two numbers to demonstrate the use cases of `dotnet watch`. The sample application contains an intentional bug that we'll fix as part of this tutorial.

## Getting started

Start by downloading [the sample application](https://github.com/aspnet/Docs/tree/master/aspnet/tutorials/dotnet-watch/sample). It contains two projects, `WebApp` (a web application) and `WebAppTests` (unit tests for the web application)

In a console, open the folder where you downloaded the sample application and run:

1. `dotnet restore`
2. `cd WebApp`
3. `dotnet run`

The console output will show messages similar to the ones below, indicating that the application is now running and waiting for requests:

````bash
$ dotnet run
Project WebApp (.NETCoreApp,Version=v1.0) will be compiled because inputs were modified
Compiling WebApp for .NETCoreApp,Version=v1.0

Compilation succeeded.
  0 Warning(s)
  0 Error(s)

Time elapsed 00:00:02.6049991

Hosting environment: Production
Content root path: /Users/user/dev/aspnet/Docs/aspnet/tutorials/dotnet-watch/sample/WebApp
Now listening on: http://localhost:5000
Application started. Press Ctrl+C to shut down.
````

In a web browser, navigate to `http://localhost:5000/api/math/sum?a=4&b=5` and you should see the result `9`.

If you navigate to `http://localhost:5000/api/math/product?a=4&b=5` instead, you'd expect to get the result `20`. Instead, you get `9` again.

We'll fix that.

## Adding `dotnet watch` to a project

1. Add `Microsoft.DotNet.Watcher.Tools` to the `tools` section of the *WebApp/project.json* file.
2. Run `dotnet restore`.

The console output will show messages similar to the ones below:

````bash
log  : Restoring packages for /Users/user/dev/aspnet/Docs/aspnet/tutorials/dotnet-watch/sample/WebApp/project.json...
log  : Restoring packages for tool 'Microsoft.DotNet.Watcher.Tools' in /Users/user/dev/aspnet/Docs/aspnet/tutorials/dotnet-watch/sample/WebApp/project.json...
log  : Installing Microsoft.DotNet.Watcher.Core 1.0.0-preview2-final.
log  : Installing Microsoft.DotNet.Watcher.Tools 1.0.0-preview2-final.
````

## Running `dotnet` commands using `dotnet watch`

Any `dotnet` command can be run with  `dotnet watch`:  For example:

<!--     Command  Command with watch  dotnet run  dotnet watch run  dotnet run -f net451  dotnet watch run -f net451  dotnet run -f net451 -- --arg1  dotnet watch run -f net451 -- --arg1  dotnet test  dotnet watch test -->

| Command | Command with watch |
| ---- | ----- |
| dotnet run  | dotnet watch run |
| dotnet run -f net451 | dotnet watch run -f net451 |
| dotnet run -f net451 -- --arg1 | dotnet watch run -f net451 -- --arg1 |
| dotnet test | dotnet watch test |

To run `WebApp` using the watcher, run `dotnet watch run` in the `WebApp` folder. The console output will show messages similar to the ones below, indicating that `dotnet watch` is now watching code files:

````bash
user$ dotnet watch run
[DotNetWatcher] info: Running dotnet with the following arguments: run
[DotNetWatcher] info: dotnet process id: 39746
Project WebApp (.NETCoreApp,Version=v1.0) was previously compiled. Skipping compilation.
Hosting environment: Production
Content root path: /Users/user/dev/aspnet/Docs/aspnet/tutorials/dotnet-watch/sample/WebApp
Now listening on: http://localhost:5000
Application started. Press Ctrl+C to shut down.
````

## Making changes with `dotnet watch`

Make sure `dotnet watch` is running.

Let's fix the bug in *WebApp/Controllers/MathController.cs* that we discovered when we tried to compute the product of two number:

[!code-csharp[Main](dotnet-watch/sample/WebApp/Controllers/MathController.cs?range=12-17&highlight=5)]

Fix the code by replacing `a + b` with `a * b`.

Save the file. The console output will show messages similar to the ones below, indicating that `dotnet watch` detected a file change and restarted the application.

````bash
[DotNetWatcher] info: File changed: /Users/user/dev/aspnet/Docs/aspnet/tutorials/dotnet-watch/sample/WebApp/Controllers/MathController.cs
[DotNetWatcher] info: Running dotnet with the following arguments: run
[DotNetWatcher] info: dotnet process id: 39940
Project WebApp (.NETCoreApp,Version=v1.0) will be compiled because inputs were modified
Compiling WebApp for .NETCoreApp,Version=v1.0
Compilation succeeded.
  0 Warning(s)
  0 Error(s)
Time elapsed 00:00:03.3312829

Hosting environment: Production
Content root path: /Users/user/dev/aspnet/Docs/aspnet/tutorials/dotnet-watch/sample/WebApp
Now listening on: http://localhost:5000
Application started. Press Ctrl+C to shut down.
````

Verify `http://localhost:5000/api/math/product?a=4&b=5` returns the correct result.

## Running tests using `dotnet watch`

The file watcher can run other `dotnet` commands like `test` or `publish`.

1. Open the `WebAppTests` folder that already has `dotnet watch` in *project.json*.

2. Run `dotnet watch test`.

    If you previously fixed the bug in the `MathController` then you'll see an output similar to the one below, otherwise you'll see a test failure:
    
    ````bash
    WebAppTests user$ dotnet watch test
    [DotNetWatcher] info: Running dotnet with the following arguments: test
    [DotNetWatcher] info: dotnet process id: 40193
    Project WebApp (.NETCoreApp,Version=v1.0) was previously compiled. Skipping compilation.
    Project WebAppTests (.NETCoreApp,Version=v1.0) was previously compiled. Skipping compilation.
    xUnit.net .NET CLI test runner (64-bit .NET Core osx.10.11-x64)
      Discovering: WebAppTests
      Discovered:  WebAppTests
      Starting:    WebAppTests
      Finished:    WebAppTests
    === TEST EXECUTION SUMMARY ===
       WebAppTests  Total: 2, Errors: 0, Failed: 0, Skipped: 0, Time: 0.259s
    SUMMARY: Total: 1 targets, Passed: 1, Failed: 0.
    [DotNetWatcher] info: dotnet exit code: 0
    [DotNetWatcher] info: Waiting for a file to change before restarting dotnet...
    ````
    
    Once all the tests run, the watcher will indicate that it's waiting for a file to change before restarting `dotnet test`.

3. Open the controller file in *WebApp/Controllers/MathController.cs* and change some code. If you haven't fixed the product bug, do it now. Save the file.

`dotnet watch` will detect the file change and rerun the tests. The console output will show messages similar to the one below:

````bash
[DotNetWatcher] info: File changed: /Users/user/dev/aspnet/Docs/aspnet/tutorials/dotnet-watch/sample/WebApp/Controllers/MathController.cs
[DotNetWatcher] info: Running dotnet with the following arguments: test
[DotNetWatcher] info: dotnet process id: 40233
Project WebApp (.NETCoreApp,Version=v1.0) will be compiled because inputs were modified
Compiling WebApp for .NETCoreApp,Version=v1.0
Compilation succeeded.
  0 Warning(s)
  0 Error(s)
Time elapsed 00:00:03.2127590
Project WebAppTests (.NETCoreApp,Version=v1.0) will be compiled because dependencies changed
Compiling WebAppTests for .NETCoreApp,Version=v1.0
Compilation succeeded.
  0 Warning(s)
  0 Error(s)
Time elapsed 00:00:02.1204052

xUnit.net .NET CLI test runner (64-bit .NET Core osx.10.11-x64)
  Discovering: WebAppTests
  Discovered:  WebAppTests
  Starting:    WebAppTests
  Finished:    WebAppTests
=== TEST EXECUTION SUMMARY ===
   WebAppTests  Total: 2, Errors: 0, Failed: 0, Skipped: 0, Time: 0.260s
SUMMARY: Total: 1 targets, Passed: 1, Failed: 0.
[DotNetWatcher] info: dotnet exit code: 0

[DotNetWatcher] info: Waiting for a file to change before restarting dotnet...
````