Usability Heuristics · heuristic
Error Prevention
Playable Play this law (~3 min)or keep reading below ↓
Better than good error messages is a design that prevents problems from occurring in the first place: constrain inputs to valid options, separate destructive actions from safe ones, confirm the irreversible, and make risky states visible before the mistake happens.
Where it comes from
Also from Nielsen's 1994 set — but the thinking goes back to Don Norman's slips-versus-mistakes distinction and to physical design: a car won't shift to reverse while driving forward, a microwave stops when the door opens, and a filing-cabinet drawer can't all open at once (it would tip). Good machines make the wrong action physically impossible; good interfaces do the same with constraints, confirmation and separation.
Origin: Interlocks and forcing functions — the car that won't reverse at speed
In the wild
- Flight date pickers
Greying out return dates before departure makes the impossible un-typeable — no validation needed.
- Gmail
'You wrote attached but there's no attachment' catches the slip in the moment it matters.
- Dangerous admin actions
'Type the project name to delete it' matches friction to stakes — trivial for intent, impossible by accident.
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