Usability Heuristics · heuristic
Help Users Recognize, Diagnose & Recover from Errors
Playable Play this law (~3 min)or keep reading below ↓
Nielsen's H9: error messages should be expressed in plain language (no error codes alone), precisely indicate the problem, and constructively suggest a solution. Recognise → diagnose → recover: the user must learn WHAT happened, WHY, and WHAT TO DO NEXT — with their work intact. An error state is a fork in trust: handled well it builds it, handled with 'Something went wrong' it burns it.
Where it comes from
Miss a highway exit and the road doesn't say 'NAVIGATION ERROR 0x404' — signage tells you where you actually are, and the next U-turn or exit is designed into the road because engineers PLAN for wrong turns. Aviation went further: after the 1977 Tenerife disaster, crew communication was rebuilt so that errors are announced in plain words and every callout includes the corrective action. H9 asks your error states to be that road, that cockpit.
Origin: The highway U-turn sign; post-Tenerife CRM callouts
In the wild
- Typo-suggesting email fields
'Did you mean @gmail.com?' recognises, diagnoses and offers the fix in one line.
- Payment failure screens
'Bank declined — try another card or UPI; your cart is saved' names the cause and both exits.
- Git's error output
Famously prints the exact command that will fix the state it just complained about.
Further reading
Don't just read it — feel it.
Play the 3-minute game and let your own reactions prove the law.
Play the lesson