Design and content
Build services that are flexible enough to allow users to give data in a way that they would naturally. For example we should allow users to enter a postcode in upper or lower case, with or without a space.
Validation messages should only be triggered on mandatory fields. They must be factual and help the user move on.
Make sure validation messages in the error box at the top of the page start with a lower case letter. Do not use full stops.
Make sure inline validation messages are sentence case (the first letter is capitalised). Do not use full stops.
Say: That’s not an email address
Do not say:
That does not look like an email address
If the input field is empty, use an imperative statement.
Say: Enter your full name
Do not say: Full name must be entered
If our systems require certain formats and the user needs to change what they’ve entered, tell them what the requirements are.
Avoid passive language.
Say: Enter the hours you work a week as a whole number, like 30
Do not say:
Hours worked a week is not valid
GOV.UK in some cases does not use the imperative form and this breaks the grammar rules following the lead-in line. We do not do that at Co-op, instead we restructure the messaging to be front-loaded with an imperative.
But the GOV.UK Design System has a long list of examples for how to handle different input requirements which you might want to refer to for inspiration.