How can I display detailed error pages in ASP.NET Core's staging environment on localhost?

You won’t see detailed error pages in staging or production by default because the built‐in behavior is to provide generic error messages in those environments. The Developer Exception Page middleware—which shows detailed errors—is only automatically added in the Development environment. That’s why you have to temporarily “trick” the application by renaming settings files to run in development mode.

There are two common approaches to troubleshoot without renaming your configuration files:

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1. Override the Error Handling in Startup/Program

You can explicitly configure your error-handling pipeline so that it shows detailed errors when running on localhost even if the environment isn’t “Development”. For example, in your Startup’s configuration you can check if you’re in staging while running locally and then add the Developer Exception Page middleware:

CSHARPCopied
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    // Option 1: Conditionally enable detailed errors when in staging on localhost.
    if (env.IsDevelopment() || (env.IsStaging() && IsLocalRequest()))
    {
        app.UseDeveloperExceptionPage();
    }
    else
    {
        app.UseExceptionHandler("/Home/Error");
        app.UseHsts();
    }

    // ... other middleware registrations
}

// A helper method to decide if the current request is local.
private bool IsLocalRequest()
{
    // Customize this check as needed. For example, you can check the request's RemoteIpAddress in middleware.
    return true;
}

Note: Be careful with this approach. You should only enable detailed errors in a secure, local-only scenario. You don’t want to accidentally expose sensitive error details to external clients.

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2. Use the ASPNETCORE_DETAILEDERRORS Environment Variable

ASP.NET Core also supports an environment variable that forces detailed error messages even when not running in Development. You can set this variable when launching your application:

• On Windows (Command Prompt):

  CMDCopied
  set ASPNETCORE_DETAILEDERRORS=true
  dotnet run --environment Staging

• On Linux/Mac (Bash):

  BASHCopied
  export ASPNETCORE_DETAILEDERRORS=true
  dotnet run --environment Staging

While this method avoids modifying your Startup code, it should only be used temporarily on your development machine. Be sure not to set this in your real staging or production environments.

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Summary

There is no built-in configuration that automatically shows detailed errors for staging or production—this is by design to protect your application from leaking sensitive error details. Instead, you’ll need to either modify your middleware to conditionally enable the Developer Exception Page or use the ASPNETCORE_DETAILEDERRORS environment variable (only on your local machine) for temporary troubleshooting.

Pick the method that best suits your troubleshooting needs, and remember to revert these tweaks once you’re done troubleshooting.