Inline form validation

A List Apart’s article on Inline Validation is one of the most informative I’ve read in a while — and it’s backed by solid data.

Some useful lessons:

1. Inline validation can reduce form completion time by 40%
2. Use inline validations where the user doesn’t know if they’ll get it wrong (e.g. is a username available?). Don’t use them if user knows the answer (e.g. their name)
3. Validate on blur, not on keypress (it’s distracting, and users can’t multitask)