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How should I formulate a validation error message for a number field?

  • A number is expected.
  • A number is required.
  • The value should be a number.
  • Number is not valid.
  • Invalid number.
  • Value is not a number.
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Why can the user input something that isn't a number? The error message should also point the field, for example: "The 'donut count' value must be a number." – Evil Closet Monkey Apr 14 '14 at 20:48
Give the solution, not the problem. – Marjan Venema Apr 15 '14 at 10:29
up vote 1 down vote accepted

There are a few things you can do up front, such as be clear that the input expects a number. Or simply not accept inputs that aren't numbers (if they type characters just ignore them).

To dissect your options a bit more:

  • Your first three (number is expected/required, value should be a number) are good. They call out that a number is something you need to enter. Fairly straightforward and appropriate if the user inputs something that is not a number.
  • The next two (number is not valid, invalid number) are less useful , as they are too vague. "Number is not valid." Does that mean I entered a number, and it's not a valid number? Tell me what IS a valid number. If I enter a character, then it's just wrong. I didn't give you an invalid number, I gave you an invalid input, that is not a number.
  • The last one is ok, but also a bit vague. "Value is not a number." Ok? Is it a problem that it's not a number? You're stating a fact about the input, when I think it could be more clear to say "Value should BE a number."
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