Fields with an imprecise data type
On a phone the wrong keyboard comes up. Typing an email address with the normal keyboard is slower and produces more typos — and a typo in the email address is a customer who never reaches you.
When we count it as met
When we measure the same pages again, no field declares a type other than the one that matches what it asks for.
How to check it yourself
Confirm it in the code of each field: its type matches what it asks for, for example email for an email address or tel for a phone number.
Measure it on your site
UXMachine measures it in a real browser, on desktop and mobile, together with the other checks.