3.3.4 Error Prevention (Legal, Financial, Data)

Some actions are difficult or impossible to reverse: making a purchase, submitting a legal document, deleting account data. For these high-stakes interactions, users must be given an opportunity to catch and correct mistakes.

At least one of three mechanisms must be provided: submissions must be reversible, inputs must be checked for errors and users given the opportunity to correct them before submission, or a mechanism is provided for the user to review, confirm, and correct before the final submission is processed.

Add a review step before final submission of any order, application, or legal form. Show all entered data and allow corrections before confirming.

For purchases, provide a confirmation page that shows the order and a clear 'Confirm order' button before the transaction is processed.

For deletions, add a confirmation step and ideally a recovery mechanism (such as a trash or recycle period).

For data modifications, provide undo functionality where possible.

• Buy now button that immediately processes payment without a review step
• Account deletion that happens immediately on click with no confirmation
• Application form that submits on the last page without a review screen