Error Prevention (All)
Where a page asks the reader to submit information, one of three things has to be true. The submission can be reversed. Or the data gets checked for errors and the reader gets a chance to correct them. Or a mechanism lets them review, confirm and correct everything before it goes. Any one is enough. At Level AA the same three alternatives apply, but only to four kinds of page. Legal commitments, financial transactions, changes to data the reader controls, and test submissions. This AAA version drops those four conditions and reaches every page asking for a submission.
Why it matters
A mistake in an ordinary form is still a mistake, and for somebody who found the form hard the first time, redoing it is exactly as hard the second time. A review step costs everybody else very little and saves those readers the whole task. There is a reason to prefer the review route over the undo route, too. Being able to reverse something in theory is not much use if reversing it is itself a difficult process, and the person who needed the safety net is the same person who will struggle to use it.
Who this rule protects
People with cognitive disabilities, people with motor disabilities who are more likely to mistype or mis-click, and honestly anybody who has ever pressed submit by mistake. W3C names transposing numbers and hitting keys by accident specifically.
How to check it yourself
- For each form, ask which of the three routes it takes. Reversible, checked, or confirmed.
- Submit with a deliberate error and see whether the form catches it and lets you fix it, which alone satisfies the rule.
- Where the route is review, check that correcting one answer does not lose the others.
- Where the route is reversible, check that the page says how long the reader has and what the procedure is.
Failures we see most often
- A long form submits on click with no validation, no review and no way back, so all three routes are missing rather than one.
- A review page shows the answers, then sends the reader back to an empty form to change one of them.
- A cancellation window exists and the page never says how long it is or how to use it.
Who this one is for
Read from this rule's own note above, so the grouping and the note cannot disagree.
- Motor and keyboard-onlypeople who cannot use a mouse, or cannot use one precisely
- Cognitive and learningpeople for whom the difficulty is understanding, remembering, or staying with it
How to fix it
- Add a check-your-answers step showing exactly what will be submitted, and let the reader change one thing and come back without losing the rest.
- Put a confirmation checkbox next to the submit button rather than wording the button more firmly. W3C's reasoning is that two separate actions force the second look and a stern label does not.
- Hold deleted data somewhere recoverable for a period instead of deleting it outright.
- Where a submission can be cancelled afterward, say how long the window is and how to do it, on the same site where it was made.
Fix guides for the related rule
Our fix guides are mapped to the 55 rules an audit tests, so none of them is filed against this enhanced criterion. W3C does document techniques for it, and the nearest work we have written up is 3.3.4 Error Prevention (Legal, Financial, Data), which asks for the same thing at a lower bar. Clearing that bar does not clear this one, so treat its 7 fix guides as the place to start rather than the answer.
Passes vs. fails
Passes
The same form validates as you go, then shows a check-your-answers page you can edit and return from.
Fails
A twelve-field inquiry form sends the moment you click submit, with nothing checked, nothing shown back and no way to withdraw it afterwards.
In audits and lawsuits
This is Level AAA and worth adopting on any form where redoing it is a real cost. Get the structure right when you assess it, because this is an at-least-one test rather than a checklist. A form that validates properly and lets the reader fix what it caught already satisfies the criterion, with no review step and no undo. Be careful too about what is already required lower down. Deleting data the reader controls sits inside criterion 3.3.4 at Level AA whatever its legal significance, so a delete that fails is an AA finding rather than an AAA one. It fails only when none of the three routes is there, so a delete with no confirmation dialog still conforms if it can be undone, or if the form catches the mistake and lets the reader fix it. W3C narrows that on the other side as well. It is about preventing mass loss of data, not about putting a confirmation on every save.