Level AA · WCAG 2.0
3.3.4 Error Prevention (Legal, Financial, Data)
A submission with legal or financial consequences, or one that changes or deletes stored data, can be reversed, is checked, or can be reviewed first.
Partly automated Some failures are detectable, others need judgement.
How it fails in practice
A checkout that places the order on the first click, with no summary to catch a wrong address. An account deletion with no confirmation and no way back. A mistyped quantity becomes a contract.
How to fix it
Put a review step before anything is committed, with every detail and a way to change it. Where that does not fit, let the action be undone for a while afterwards. One of the three — reversible, checked, confirmed — is enough.
At a glance
- Level
- Level AA — the level EN 301 549 requires, and therefore the level the BFSG and the EAA are measured against.
- Principle
- Understandable
- Guideline
- 3.3 Input Assistance
- Added in
- WCAG 2.0
- EN 301 549
- 9.3.3.4
- Automated check
- Partly automated
How to test it by hand
- List every form that commits something: an order, a booking, a contract, a payment, a change to an account, a deletion.
- Walk each one to its last step without submitting. There is a summary to check and correct before the final confirm — or, failing that, a clear way to undo afterwards.
- Enter a mistake on purpose — a wrong quantity, a mistyped address — and continue, on a test account where one exists. It is caught, or visible on the review step, before anything is committed.
In code
<form action="/order" method="post">
<!-- address, payment details… -->
<button>Place order</button> <!-- charges the card on this click -->
</form><form action="/order/review" method="post">
<!-- address, payment details… -->
<button>Review order</button>
</form>
<!-- /order/review -->
<h2>Check your order</h2>
<dl>
<dt>Delivery address</dt>
<dd>12 Market Street, Leeds <a href="/checkout/address/">Change</a></dd>
</dl>
<form action="/order" method="post"><button>Place order</button></form>Partly automated
How far an automated check gets
A tool finds some failures here and cannot see the rest. A clean automated result means the checks that exist found nothing — not that the criterion is met. This is the gap that makes a green scan look like an accessible site, and it is where the keyboard agent, the agents still in development and a human reviewer do the remaining work.
Related criteria
Other criteria under the same guideline.
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