A good error message has three parts:
- The problem – explains that an error has happened;
- The cause – explains what caused the problem;
- The solution – explains how to overcome the problem.
After you ensure your message contains all these three parts, its time to review it. You need to edit it to ensure it:
- Is user centred – avoid jargon and words your audience will have an hard time understanding;
- Is direct – as William Strunk said, “Put statements in positive form. Avoid tame, colourless, hesitating and non-committal language”;
- Omits needless words – cut, cut, cut.
Source: How to Write Error Messages