This micro-demo compares naggy validation (error flashes while you’re still typing) vs polite validation (waits until blur or after a short pause). Try typing alex@example.com.
Rapidly changing error messages can be distracting, and for some assistive tech users it can create repeated announcements. A common pattern is: validate on blur, or validate after a short debounce (and don’t mark the field invalid until the user is done typing).