Usability · Applied
Error Prevention
Prevent predictable mistakes before relying on error messages.
5 minute field note
Helps create
Fewer costly mistakes
Overview
Make the interface carry more of the effort.
Constrain invalid actions, clarify consequences and preserve recovery paths for errors that cannot be prevented.
Human impact
Why it matters
Prevent predictable mistakes before relying on error messages. When the interface does not account for this, people spend effort interpreting the product instead of completing the task. Applied with context, the principle supports fewer costly mistakes without removing meaningful choice or control.
Design hypothesis
If we apply Error Prevention to the decision point, people should reach fewer costly mistakes with less avoidable friction.
Mechanism
How it works
Notice where the task currently asks people to forms or validation without enough support.
Constrain invalid actions, clarify consequences and preserve recovery paths for errors that cannot be prevented.
Make the smallest change that should improve fewer costly mistakes, then compare the task before and after.
Interactive experiment
Which safety strategy fits each consequence?
Quarterly report
Shared with the Operations team · updated today
Turn the experiment into a decision
What happened
Constraints prevent invalid states, confirmations slow consequential actions and undo supports quick recovery.
Why it happened
Different mistakes carry different likelihood, severity and recovery costs.
Where to apply it
Publishing, payments, destructive actions, form input and bulk record changes.
How to validate it
Track prevented errors, unnecessary interruptions, recovery success and repeated mistakes.
Decision guide
When to use it
Apply it
Practical checklist
State requirements before input.
Validate near the field at the right time.
Disable only when the reason is visible.
Confirm rare, consequential and irreversible actions.
Watch for
Common mistakes
Validating every keystroke aggressively.
Clearing valid input after one error.
Using generic messages that do not explain recovery.
Accessibility considerations
Connect errors to their fields programmatically.
Move focus carefully and provide an error summary for long forms.
Evidence plan
How to test it
Run a short task-based usability test.
Give five representative people one realistic goal. Watch without teaching, record the first hesitation or error and ask what they expected after the task.
Observe
Completion, hesitation, recovery and whether the system response matches the person’s expectation.
Decide
Keep the change when it improves fewer costly mistakes without creating a new failure elsewhere.
Use with judgment
Limits and trade-offs
Error Prevention is a decision lens, not a universal prescription. Context, frequency, expertise and consequence can change the right implementation.
Optimising only for fewer costly mistakes can create new costs elsewhere. Recheck access, comprehension, user control and business constraints together.
A polished prototype can still fail in real use. Validate consequential decisions with representative people and realistic content.
Design responsibly
Better outcomes must also be honest outcomes.
Use the principle to reduce avoidable effort, not to pressure people into a choice.
Keep price, risk, consent and irreversible consequences visible before commitment.
Record what evidence supports the decision and what remains an assumption.
Evidence
Sources and interpretation
Design principles are lenses, not automatic answers. Apply them in context and validate consequential decisions with users and accessibility testing.
Keep close
Key takeaways
Prevent predictable mistakes before relying on error messages.
State requirements before input.
Keep the change when it improves fewer costly mistakes without creating a new failure elsewhere.