Inline validation: pros and cons

Inline validation: benefits (advantages) and costs (disadvantages)

If you’ve read our article about research into inline validation you have found that ….

There are some. A comparison.


Helps with tricky fields. Appreciated by users for fields which they want to provide extra thought and care (username, password) or are tricky to fill in (bank account and credit card numbers) or are typically written in various forms.
Immediate help. Appreciated by users because form completion time can be shortened due to immediate feedback. Users remembered what they just typed, so they are in the flow of providing that data and are also more capable of correcting it.
Motivation. Encourages the user by affirming that everything is correct and that he will not remain in the same page but arrive at the next page after clicking the submit button.
– Shorter forms. With inline validation error messages will usually appear next to rather than under fields, depending on where error messages appear. On the other hand, if there are 2 fields placed next to eachother and they are both wrong, how and where will system communicate this?


Cost. Can be expensive to implement (server-side).
System performance. Inline validation may lead to larger scripts, server slow-downs (if error rate is high) 
– SEO. More Javascript may mean heavier, more complex pages. Google might rate your form page lower.
– Expertise. If not designed properly can harm usability and conversion. Also testing intensive.
Leads. May harm lead capturing and lead conversion (especially if user encounters an error, is discouraged to continue filling in the form)
Surprise and distractions. Users don’t know that their form is being validated until they notice a checkmark or error message. Badly designed checkmarks are interpreted with confusion, so it needs to be clear what they represent to be understood. Clicking Submit must scroll the browser window to show where the first error is.
Disrupting. Completion mode versus revision mode theories tell us that interupting a user interupts his mental flow (especially for those users who hardly look up to the screen from their keyboard). Does this lead to increased form completion time? 
Conversion benefit unknown. Requires A/B split testing to determine if it really makes a difference on conversion without doing too much harm to gaining leads.


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