We use two types of error messages – alerts (boxes that pop up out of the form or page) and inline errors (error messages that appear by the incorrectly filled form field).

Alerts

Alerts should lead in with a simple statement of fact, followed by a broad description of the options available on the page. For example, "It looks like your income could run out when you're 78.”

If you want your income to last longer, you could lower your monthly income or move more money into this pot".

Avoid stating whether an alert is positive or negative. In the example above, it would be wrong to say "There's a problem - your money might run out when you're 78. To fix this, (...)" – as it's impossible to know the user's future plans or overall financial situation.

Inline errors

Unlike regular error messages/alerts, inline error messages don't necessarily need to explain what went wrong. Telling the user the solution is often enough to prompt them to correct the error, especially in simple forms. For example, "Please enter your name" is enough to prompt a user to fill in a form field they accidentally missed.

Explaining the error can make the message unnecessarily long and harder to read. For example, "You didn't enter your name. Please enter your name" is overkill for a simple to understand and easy to fix error.