Username Online is an OSINT-focused service that helps users check whether a username is already in use across popular websites. By searching multiple platforms, it gives individuals and researchers a convenient way to assess username availability and find existing online profiles. Users can check up to 10 usernames at once, with results organized by site and status to make the search easier to review.

The service includes categories covering areas such as social media, gaming, business, finance, technology, news, shopping, and more, with options to include or exclude NSFW sites. Username Online also offers mobile apps for iOS and Android, allowing users to access its username-checking tools on the go. The service is based on the linked_services WhatsMyName repository.

Designed to save time during online research, Username Online brings multi-site username checks together in one place. It can be useful for OSINT practitioners as well as people who want to see where a particular username may already appear online