Why a friendlier message beats the generic default
On a shared form, the default error message that appears when someone breaks an input rule rarely explains what went wrong. Replacing it with specific wording -- like "Enter a number 0 or greater" instead of "This value doesn't match the data validation restrictions" -- makes the form far easier for other people to fill out correctly.
It works with any validation rule you set up
A custom error message isn't tied to one particular validation type -- it works the same way whether the underlying rule is a whole-number range, a date range, a dropdown list, or a custom formula. Once you write the message, it appears automatically any time that specific rule is broken, no matter which validation type is behind it.
Frequently Asked Questions
Can I also choose the alert style?
Yes. You can pick from three styles -- "Stop" (blocks the entry entirely), "Warning," or "Information" -- so you can match the strictness of the alert to the situation.
What happens if I leave the message blank?
If you leave the title and message fields empty, Excel falls back to showing its generic default error message instead.