Design Availability Checks for Names and Handles

Forms & Inputs · forms, validation, latency

Updated 2026-08-04

Check availability while the user types rather than after they submit. Discovering a taken handle at the end of a sign-up form is a re-entry, and discovering it inline is a keystroke.
Wait for a pause before checking, and cancel outstanding requests. A check per keystroke wastes requests and can display the answer to a value the field no longer holds.
Show four states clearly, because the middle two are what make the field feel reliable:

Never let a stale answer stick. If the value changes while a check is in flight, clear the result rather than leaving a green tick on a different word.
Re-check at submit and expect it to sometimes fail. Availability is only true at the moment it was measured, and someone else can register the name in between.
Handle the false alarm gracefully. Fast checks are often built on a Bloom filter, which can report taken when the name is actually free, so a name that fails inline should still be verified properly before the user is refused.
Validate the rules before checking the database. Length, allowed characters, and reserved words are decided locally and instantly, so do not spend a network request to say the name is too short.
Offer suggestions that are already verified as free. Proposing three alternatives that turn out to be taken is worse than proposing none.
Say why a name is unavailable when it is reserved rather than taken. System words and trademarks are refusals users cannot resolve by trying harder.

An availability check is a promise about a shared namespace, and its job is to be fast, current, and honest about which of those it is.