What it is
Finds the social accounts a site says are its own, by reading its meta tags, structured data and rel="me" links, then looks each one up on the network itself. Bluesky is also checked against the domain directly, because there a handle can be the domain name. Every lookup uses free, public endpoints, so no API keys or accounts are needed.
Why it matters
Confirms that the accounts a website points to actually exist, and that they point back to the website in return. A mismatch is worth knowing about: phishing pages routinely claim the social accounts of the brand they impersonate, and a link that only goes one way proves nothing about who owns the account.