UUID Lookup
Enter a Java Edition username to get their UUID, or paste a UUID to reverse it back to a username. Also calculates the offline-mode UUID for servers running without Mojang authentication.
Why UUIDs matter
Minecraft servers don't actually track players by name. Under the hood, every premium Java account has a UUID - a 32-character hex string that Mojang assigns once and never changes, even if you rename your account a hundred times. That's why renaming doesn't wipe your stats, inventory, or permissions: the server sees the same UUID either way.
The format you'll see most often looks like this: 069a79f4-44e9-4726-a5be-fca90e38aaf5. That's Notch's UUID - same as it was in 2012, same as it'll be in 2030. The dashes are just formatting; the raw form is 32 hex digits with no separators.
Online-mode UUID
The UUID assigned by Mojang to a paid account. Fetched from api.mojang.com at login time and verified against Mojang's session servers. This is what the vast majority of servers use.
If you're running a premium server (the default), every UUID you deal with is an online-mode UUID. Bans, whitelists, LuckPerms, CoreProtect, Dynmap - all of them use this.
Offline-mode UUID
When a server runs with online-mode=false in server.properties, it can't contact Mojang's auth servers - so it generates a UUID locally instead. The algorithm is deterministic: it hashes the string OfflinePlayer:<username> using UUID v3 (MD5-based).
The same username will always produce the same offline UUID, but it won't match the account's real online UUID. If you ever switch a server from offline to online mode, all player data needs migrating.