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Custom Error Pages

Cofoundry automatically bootstraps the ASP.NET Core error handling middleware to provide you with friendly error pages out of the box for exceptions and for other error status codes such as 404s.

The Developer Exception Page

By default, when running in the development environment, Cofoundry will automatically add the developer exception page to give you detailed information on exceptions.

This behavior can be overridden using the Cofoundry:Debug:DeveloperExceptionPageMode setting, which can have the values "DevelopmentOnly", "On" or "Off".

Example appsettings.json

  "Cofoundry": {
    "Debug": {
      "DeveloperExceptionPageMode": "On"

Customizing the Error Page

By default the built-in error page will use your default layout page to render in, but typically you'll want to override this and have your own page with custom text and styles.

Cofoundry lets you customize a handful of different error pages. Each one should be placed in your 'Views/Shared' folder, where it will be automatically discovered.

Generic Error

Unless you specify other error view files, all errors will display the generic error page. To override this built-in view you should create a file named Error.cshtml, which can use the IErrorPageViewModel as the model.

@model IErrorPageViewModel

<div class="container">

    <h1>Error: @Model.StatusCodeDescription</h1>

    <p>Uh oh! There's been an error!</p>


Not Found (404)

By default 404 errors are displayed using the generic error view, but often you'll want to create a specific view for this common type of error. To do this create a file named NotFound.cshtml, which can use INotFoundPageViewModel as the model.

@model INotFoundPageViewModel

<h1>Not Found</h1>

    Sorry, the page <strong>@Model.Path</strong> could not be found

In your controllers you can also take advantage of the INotFoundViewHelper to return a 404 result. This has the added benefit of checking for Rewrite Rules and automatically redirecting:

using Cofoundry.Web;

public class ProductController : Controller
    private readonly INotFoundViewHelper _notFoundViewHelper;
    private readonly IProductRepository _productRepository;

    public ProductController(
        INotFoundViewHelper notFoundViewHelper,
        IProductRepository productRepository
        _notFoundViewHelper = notFoundViewHelper;
        _productRepository = productRepository;

    public async Task<ActionResult> Details(int id)
        var product = _productRepository.GetById(id);

        if (product == null)
            return await _notFoundViewHelper.GetViewAsync();

        return View(product);

Other Status Codes

You can add custom error pages for other http status codes by creating a file using the status code as the name, e.g. 400.cshtml or 418.cshtml which can use IErrorPageViewModel as the model.