Inline validation considered harmful
Just kidding, this article didn't really use that word. And rather than an alarmist view, this is a fairly measured take. However, most of the arguments are actually against realtime (onblur) validation, not inline validation.
I spent two years dealing with some serious problems that were born entirely out of the fact that an application used realtime+inline validation. And that was primarily in a series of wizard-like dialogs, which really didn't make any sense (the pattern of "disable the continue button until validation is cleared" would've worked well).
Our problems included:
- forms that didn't require a certain order to filling them out, but validation that did
- false positives triggered by mouse actions that left users in an unresolvable state if they clicked "wrong"
- field groups often in a false-positive state (point #4 in the article)
This isn't the same as saying that per-field validation is wrong, and I still strongly believe in that, but this article has a lot of solid points.