Help users recognize, diagnose, and recover from errors

The law

When something goes wrong, the product should say so in plain language, explain what the problem is and offer a way to fix it.

The heuristic names three steps. People must notice the error, understand what caused it, and know what to do next. A message that fails any one of them leaves people stuck.

Where it comes from

This is the ninth of Jakob Nielsen's ten usability heuristics, listed in Nielsen Norman Group's 10 Usability Heuristics for User Interface Design in the form Nielsen published in 1994. Nielsen Norman Group's error-message guidelines give detailed advice on visibility, wording and recovery.

Concern with error messages is as old as interactive computing. Early systems reported errors with codes meant for programmers, and much of the early usability literature argued for messages written for the people actually using the system.

What it means for an interface

• Make errors visible. Show the message next to where the problem is, with enough contrast and an icon, not only a red border.
• Use plain language. Say what happened in words people understand, without codes or blame.
• Be specific. "Enter a date after today" is useful; "Invalid input" is not.
• Offer a way forward. Suggest the fix, keep everything people typed, and provide a link or action when the fix is elsewhere.

Examples

Form validation. A form that highlights the one field with a problem, explains the expected format beside it, and keeps all other input, lets people fix the issue in seconds.

Payment failures. "Your card was declined. Try another card or contact your bank" is better than "Error 402", and better still if the alternative payment options are right there.

Search with no results. "No results for 'runing shoes'. Did you mean 'running shoes'?" recognizes, diagnoses and offers the recovery in one line.

Where it is misapplied

• Blaming people. Messages that say people did something "invalid" or "illegal" add stress without helping.
• Vague friendliness. "Oops, something went wrong" is plain but not specific. It tells people nothing they can act on.
• Errors far from the problem. A message at the top of a long form, with no link to the field, makes people hunt for it.
• Clearing input. An error that resets the form turns a small problem into a large one.

Checklist

• Error messages appear next to the element that caused them.
• Each message says what happened and what to do, in plain words.
• Errors are shown with text and an icon, not colour alone.
• Input is preserved when an error is shown.
• System errors offer a next step, such as retry, an alternative or a contact.

Related

• Error prevention: the best error message is the one that never needs to appear.
• User control and freedom: undo is often the simplest recovery.
• Postel's Law: accepting more input formats avoids many errors entirely.
• Patterns: Inline Validation.
• Course: Heuristic evaluation.
• Pillar: UX audit.