What are your thoughts on a multi-level validation. To me, flagging ‘input is too short’ as an error while I’m still typing it is a bit annoying. What if you had valid, warn, and error states. The warn state would offer you guidance on the conditions of validation rather than telling you you’re wrong from the outset. For example with a field that needs to be a certain length:

OnFocus = (valid) No message

OnChange = (warn) At least 6 characters

OnBlur = (invalid) This field must be at least 6 characters

It’s more complex but it also does away with one of my pet peeves, entering a field only to be met with a warning that I failed to satisfy requirements that I wasn’t given up front.