What we check
We read every JSON-LD block on the page and compare each type and property with the official schema.org vocabulary, so misspelled or made-up labels are caught. For businesses we also check for the details Google expects (name, full address, phone, website, opening hours) and that the phone number in the markup matches the page.
Errors, fixes and tips
Errors mean search engines will ignore part or all of the markup. Fixes are missing details worth adding. Tips are optional improvements.
Limits
Markup added by scripts after the page loads, and older microdata, aren't checked in detail. Use Google's Rich Results Test to confirm what Google itself sees.