The guideline
Write every error message to do three things: identify which field failed, state what is wrong with it in plain language, and say what a valid value looks like. Never rely on a generic message like "Invalid input" or a bare red border with no text. Place the message immediately next to the field it concerns (or link a top-of-form summary to each field), keep it on screen until the specific problem is corrected — not on a timer — and associate it with the field via aria-describedby so assistive technology announces it. Where a correction is knowable (a mistyped domain, a value outside an allowed range), suggest it rather than only naming the failure. Where a short message cannot explain the rule in full, link it to a fuller explanation beside the field or in help instead of cramming the detail in.
Common failures
- Form error messages are vague ("Error", "Invalid input") and not anchored to specific fields.
Where it applies
Pages
Disciplines
Devices
Why it matters, how to fix it, and the research behind it
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