Inline field validation beats on-submit modal errors by a median 4.1% form-completion uplift.

Inline field validation beats on-submit modal errors by a median 4.1% form-completion uplift.
Pooled across 9 form tests, fixed-effects meta-estimate, 95% CI roughly 2.0-6.2%.
Inline corrects errors at the point of failure; modals make users re-find the bad field after a full-page reject. Cognitive cost of re-orientation is the killer.
— On-submit modal ▮▮▮▮ completion
— Inline ▮▮▮▮▮▮ completion
Exception: don't fire inline errors on every keystroke — validate on blur, not on input.
Read the number, not the story. [n=9 tests · 95% CI]