senchalabs/connect — pull request #1024 by ForbesLindesay (2014-03-15 18:52:53+00:00)
Title: Use text/plain as the content type of error messages

There are two advantages to this:

1. You don't need to use escape-html on error messages
2. Newlines in error messages and stack traces are visible to the user.

Point 2 is a massive benefit to how quick and easy it is to see error messages.