Generic validators check syntax; this audit checks the rules Google applies to local business markup: self-serving stars, hours format, placeholder contact data, address and coordinate sanity, and whether the phone in the JSON-LD matches the one visitors see.
Read the story behind this tool: Why Local Schema Validity Audit exists.
Related: Schema.org / JSON-LD Validator / NAP Consistency Checker / Schema Fix Bundle
Paste the page that carries the business markup, usually the home page or the contact page. The audit reads every JSON-LD block on it.
Used only to decide whether a rated business node is the site's own brand (self-serving) or a third party the page reviews.