Webfinger allows users to query email addresses and discover additional information about users online. It works by sending an HTTP request to a user's domain to retrieve an XRD document with links to the user's profile pages, OpenID identifier, and other information. This enhances OpenID login by allowing users to be discovered and logged in automatically. Early adopters like Google are implementing Webfinger to return profile information for Gmail addresses. Libraries like Redfinger and hCard make it easy to retrieve and parse Webfinger data in applications. Webfinger combined with protocols like Salmon also enable cross-posting of updates to multiple social networks from a single site.