Can I get Heroku Logs to return only lines outlining errors?
Try this:
heroku logs -t | grep 'error'
To get a running list of errors as and when they occur.
The inverted commas around 'error'
did it for me.
heroku logs | grep -i error
You can also install the New Relic add-on, which reports detailed error traces. I've heard good things about Loggly, too.
See also heroku - how to see all the logs
Personally I think that logs aren't the best place to look as the error and the detail are easily missed. I would ensure that my code was raising errors to an external location to ensure that they don't get missed.
There's a number of options ranging from the simple ExceptionNotifier, to more advanced systems such as Airbrake (which is what I use myself).
Not only will these notify you of the errors, but they'll also given you a stack of meta information that you can use.