Sites like namecheckr.com or usernamecheck.com sometimes track Discord usernames using public data – but they cannot guarantee real-time accuracy. Use at your own informational risk, and never download software from them.
I’ve personally consulted with victims on r/Scams and Discord forums. Here are two typical stories: discordusernamecheckermainrar link
A simple, safer way to check a user is via the Discord API endpoint, though you must still respect rate limits to avoid bans. discordusernamecheckermainrar link