[View or download sample code](https://github.com/aspnet/Docs/tree/master/aspnetcore/fundamentals/environments/sample) ([how to download](xref:tutorials/index#how-to-download-a-sample))
ASP.NET Core reads the environment variable `ASPNETCORE_ENVIRONMENT` at application startup and stores that value in [IHostingEnvironment.EnvironmentName](/dotnet/api/microsoft.aspnetcore.hosting.ihostingenvironment.environmentname?view=aspnetcore-2.0#Microsoft_AspNetCore_Hosting_IHostingEnvironment_EnvironmentName). `ASPNETCORE_ENVIRONMENT` can be set to any value, but [three values](/dotnet/api/microsoft.aspnetcore.hosting.environmentname?view=aspnetcore-2.0) are supported by the framework: [Development](/dotnet/api/microsoft.aspnetcore.hosting.environmentname.development?view=aspnetcore-2.0), [Staging](/dotnet/api/microsoft.aspnetcore.hosting.environmentname.staging?view=aspnetcore-2.0), and [Production](/dotnet/api/microsoft.aspnetcore.hosting.environmentname.production?view=aspnetcore-2.0). If `ASPNETCORE_ENVIRONMENT` isn't set, it will default to `Production`.
* Calls [UseDeveloperExceptionPage](/dotnet/api/microsoft.aspnetcore.builder.developerexceptionpageextensions.usedeveloperexceptionpage?view=aspnetcore-2.0#Microsoft_AspNetCore_Builder_DeveloperExceptionPageExtensions_UseDeveloperExceptionPage_Microsoft_AspNetCore_Builder_IApplicationBuilder_) and [UseBrowserLink](/dotnet/api/microsoft.aspnetcore.builder.browserlinkextensions.usebrowserlink?view=aspnetcore-2.0#Microsoft_AspNetCore_Builder_BrowserLinkExtensions_UseBrowserLink_Microsoft_AspNetCore_Builder_IApplicationBuilder_) when `ASPNETCORE_ENVIRONMENT` is set to `Development`.
* Calls [UseExceptionHandler](/dotnet/api/microsoft.aspnetcore.builder.exceptionhandlerextensions.useexceptionhandler?view=aspnetcore-2.0#Microsoft_AspNetCore_Builder_ExceptionHandlerExtensions_UseExceptionHandler_Microsoft_AspNetCore_Builder_IApplicationBuilder_) when the value of `ASPNETCORE_ENVIRONMENT` is set one of the following:
The [Environment Tag Helper ](xref:mvc/views/tag-helpers/builtin-th/environment-tag-helper) uses the value of `IHostingEnvironment.EnvironmentName` to include or exclude markup in the element:
Note: On Windows and macOS, environment variables and values are not case sensitive. Linux environment variables and values are **case sensitive** by default.
The development environment can enable features that shouldn't be exposed in production. For example, the ASP.NET Core templates enable the [developer exception page](xref:fundamentals/error-handling#the-developer-exception-page) in the development environment.
The environment for local machine development can be set in the *Properties\launchSettings.json* file of the project. Environment values set in *launchSettings.json* override values set in the system environment.
When the application is launched with [dotnet run](/dotnet/core/tools/dotnet-run), the first profile with `"commandName": "Project"` will be used. The value of `commandName` specifies the web server to launch. `commandName` can be one of :
Changes made to project profiles may not take effect until the web server is restarted. Kestrel must be restarted before it will detect changes made to its environment.
> *launchSettings.json* shouldn't store secrets. The [Secret Manager tool](xref:security/app-secrets) can be used to store secrets for local development.
The production environment should be configured to maximize security, performance, and application robustness. Some common settings that differ from development include:
It's often useful to set a specific environment for testing. If the environment isn't set, it will default to `Production` which disables most debugging features.
To set the `ASPNETCORE_ENVIRONMENT` for the current session, if the app is started using [dotnet run](/dotnet/core/tools/dotnet-run), the following commands are used
These commands take effect only for the current window. When the window is closed, the ASPNETCORE_ENVIRONMENT setting reverts to the default setting or machine value. In order to set the value globally on Windows open the **Control Panel** > **System** > **Advanced system settings** and add or edit the `ASPNETCORE_ENVIRONMENT` value.
See the *Setting environment variables* section of the [ASP.NET Core Module configuration reference](xref:host-and-deploy/aspnet-core-module#setting-environment-variables) topic.
To set environment variables for individual apps running in isolated Application Pools (supported on IIS 10.0+), see the *AppCmd.exe command* section of the [Environment Variables \<environmentVariables>](/iis/configuration/system.applicationHost/applicationPools/add/environmentVariables/#appcmdexe) topic.
Machine level environment variables are set in the *.bashrc* or *.bash_profile* file. Edit the file using any text editor and add the following statment.
For Linux distros, use the `export` command at the command line for session based variable settings and *bash_profile* file for machine level environment settings.
When an ASP.NET Core app starts, the [Startup class](xref:fundamentals/startup) bootstraps the app. If a class `Startup{EnvironmentName}` exists, that class will be called for that `EnvironmentName`:
[Configure](/dotnet/api/microsoft.aspnetcore.hosting.startupbase.configure?view=aspnetcore-2.0#Microsoft_AspNetCore_Hosting_StartupBase_Configure_Microsoft_AspNetCore_Builder_IApplicationBuilder_) and [ConfigureServices](/dotnet/api/microsoft.aspnetcore.hosting.startupbase.configureservices?view=aspnetcore-2.0) support environment specific versions of the form `Configure{EnvironmentName}` and `Configure{EnvironmentName}Services`:
