When things go wrong.
WHAT AN ERROR MESSAGE MUST DO
Say what happened Say what to do about it Preserve what the person had entered
THAT THIRD POINT
Losing entered data is the most damaging failure an interface can inflict.
WHAT A BAD MESSAGE LOOKS LIKE
Technical detail the person cannot act on Blame Vagueness A code with no explanation
WHAT A GOOD ONE LOOKS LIKE
Plain language, specific, with a next step.
WHERE TO PUT IT
Next to what caused it, and summarised at the top if there are several.
WHAT TONE TO USE
Neutral and helpful.
Not apologetic, not humorous, not accusing.
WHAT TO DISTINGUISH
Something the person can fix Something they cannot
WHAT TO DO ABOUT THE SECOND
Say so, and say what happens next.
WHAT TO AVOID
Hiding errors Clearing the form Errors that appear only after submission when they could be checked earlier
WHAT TO LOG
The technical detail, for you.
