Better Errors

Better Errors replaces the standard Rails error page with a much better and more useful error page. It is also usable outside of Rails in any Rack app as Rack middleware.

Features

For screenshots of these features, see the wiki.

Full stack trace
Source code inspection for all stack frames (with highlighting)
Local and instance variable inspection
Live shell (REPL) on every stack frame
Links directly to the source line in your editor
Useful information in non-HTML requests

Installation

Add this to your Gemfile:

group :development do
  gem "better_errors"
  gem "binding_of_caller"
end

binding_of_caller is optional, but is necessary to use Better Errors' advanced features (REPL, local/instance variable inspection, pretty stack frame names).

Note: If you discover that Better Errors isn't working - particularly after upgrading from version 0.5.0 or less - be sure to set config.consider_all_requests_local = true in config/environments/development.rb.

Security

NOTE: It is critical you put better_errors only in the development section of your Gemfile. Do NOT run better_errors in production, or on Internet-facing hosts.

You will notice that the only machine that gets the Better Errors page is localhost, which means you get the default error page if you are developing on a remote host (or a virtually remote host, such as a Vagrant box). Obviously, the REPL is not something you want to expose to the public, and there may be sensitive information available in the backtrace.

For more information on how to configure access, see the wiki.

Usage

If you're using Rails, there's nothing else you need to do.

Using without Rails.

If you're not using Rails, you need to insert BetterErrors::Middleware into your middleware stack, and optionally set BetterErrors.application_root if you'd like Better Errors to abbreviate filenames within your application.

For instructions for your specific middleware, see the wiki.

Plain text requests

Better Errors will render a plain text error page when the request is an XMLHttpRequest or when the Accept header does not include 'html'.

Unicorn, Puma, and other multi-worker servers

Better Errors works by leaving a lot of context in server process memory. If you're using a web server that runs multiple "workers" it's likely that a second request (as happens when you click on a stack frame) will hit a different worker. That worker won't have the necessary context in memory, and you'll see a Session Expired message.

If this is the case for you, consider turning the number of workers to one (1) in development. Another option would be to use Webrick, Mongrel, Thin, or another single-process server as your rails server, when you are trying to troubleshoot an issue in development.

Changing the link to your editor

Better Errors includes a link to your editor for the file and line of code that is being shown. By default, it uses your environment to determine which editor should be opened. See the wiki for instructions on configuring the editor.

Get in touch!

If you're using better_errors, I'd love to hear from you. Drop me a line and tell me what you think!

Contributing

Fork it
Create your feature branch (git checkout -b my-new-feature)
Commit your changes (git commit -am 'Add some feature')
Push to the branch (git push origin my-new-feature)
Create new Pull Request