Instead of having a Regex that searches for error|critical|except it’s a good thing to have a log level in your logging infrastructure, so that you can query for example log level=2 and get all the bad things.

It takes a bit to work this into the code and infrastructure everywhere but it’s worth it.

In Ruby:

    %w[fatal invalid unknown error except critical cannot].any? {|word| 'My critical error message'.include? word}

... may be better than a regex if it's just a list of literal strings. Javascript also has something similar.

watch out for someone writing [FATAL] in a form somewhere and it getting logged :)

That's a smell. If you have to type a mouthful like that more than twice, put it in a script.