I love this. I think it would be useful to move the debugging chapter much earlier in the book. Presumably, new users of Flask will encounter the (pretty awesome) Werkzeug error page as they move through the book. It might work well if a debugging chapter had exposed them to a little bit of how to interpret and use that tool. I'm sure there's a lot more about debugging to cover so maybe splitting things up makes sense too.
Perhaps a link somewhere to what this 'flask' thing actually is on either your repo or the page you linked to would be appreciated by people like myself who have no clue what you're writing a book about in the first place?
Thanks for posting this!<p>I'm the author if anyone has any questions. If you have some feedback, I'm looking forward to seeing bug reports on GitHub: <a href="https://github.com/rpicard/explore-flask" rel="nofollow">https://github.com/rpicard/explore-flask</a>