It parses your JSON-LD and checks it against the schema.org shape: required fields, valid types, and the structural mistakes that make a block unusable.

The validator reports each problem with the property at fault. Most fixes are small: a missing required field, a wrong type name, or a mistyped property. Re-run after fixing.

A malformed block is worse than none: engines that cannot parse it will ignore it, and the page ships dead weight. Validation is the five-minute check before deploy.