Minecraft Offline UUID Generator
The exact UUID an offline-mode (cracked) server gives a name — worked out in your browser, with no lookup and no name sent anywhere.
Everything here is computed locally with an MD5 written into the page — no input data ever leaves the page, so it also works offline. Names are case-sensitive: Notch and notch get different UUIDs.
How Minecraft builds an offline-mode UUID
When a server runs with online-mode=false, nobody checks the joining player against Mojang, so the server cannot be told what their UUID is. It invents one from the only thing it has — the name they typed:
- Join the text OfflinePlayer: to the username exactly as typed, giving e.g. OfflinePlayer:Notch.
- Take the MD5 of those UTF-8 bytes: 16 bytes of hash.
- Overwrite the top half of byte 6 with 3 (the version nibble) and force the top two bits of byte 8 to 10 (the RFC 4122 variant).
- Print it as hex with the usual 8-4-4-4-12 dashes.
That is exactly Java's UUID.nameUUIDFromBytes, which is what vanilla, Spigot, Paper, Fabric and Forge all call. The result is a version 3 UUID — you can spot one by the 3 at the start of the third group. Because the recipe is fixed, the same name gives the same offline player UUID on every cracked server that has ever run.
Using an offline UUID in whitelist.json and ops.json
Both files sit next to server.properties in the server folder, and both match players by UUID rather than by name. On an offline-mode server the UUID they need is the one above, not a Mojang one — paste a Mojang UUID into an offline whitelist and the player is never recognised.
- Stop the server. Editing these files while it runs gets your changes overwritten on shutdown.
- Paste the generated block over the whole file, or merge the entries into the existing array.
- Start the server, or run /whitelist reload if it is already up.
The same UUIDs go into banned-players.json, into world/playerdata/<uuid>.dat, and into most plugin databases — LuckPerms, Essentials and CoreProtect all key on it. If a player renames on a cracked server they become a brand new person with an empty inventory, because the name is the identity.
Cracked server UUIDs and what they cannot do
| Offline mode | Online mode | |
|---|---|---|
| UUID version | 3 (name hash) | 4 (random, issued by Mojang) |
| Where it comes from | MD5 of the name | Mojang's account records |
| Survives a rename | No — new name, new player | Yes |
| Proves who you are | No | Yes |
Nothing verifies a name in offline mode, so anyone who types a whitelisted username gets that username's UUID and walks in with its permissions and its inventory. Treat an offline whitelist as a convenience, not a lock, and put a login plugin in front of it if accounts matter. Switching online-mode later re-identifies everyone: budget an afternoon for migrating player data, and take a backup first.
FAQ
How does Minecraft generate an offline UUID?
It takes the text OfflinePlayer: followed by the exact username, hashes those bytes with MD5, then overwrites the version nibble with 3 and sets the two RFC 4122 variant bits. That is what Java's UUID.nameUUIDFromBytes does, so the answer is a version 3 UUID and it is identical on every offline-mode server in the world.
Is an offline UUID case-sensitive?
Yes. Notch and notch are different strings, so they hash to completely different UUIDs. Type the username exactly as the player types it at the login screen, capitals and underscores included, or the whitelist entry will not match them.
What happens to player data when I switch online-mode?
Everyone gets a different UUID, so inventories, advancements, ender chests, permissions, homes and balances all look wiped. Nothing is actually deleted — the old playerdata files are still in the world folder under the old UUID, they are just no longer matched to anybody.
Can two people end up with the same offline UUID?
Anyone who types a given username gets that username's UUID, because nothing is verified against Mojang. An offline whitelist therefore keeps out only people who have not guessed a listed name — it is a speed bump, not authentication. Use a login plugin if accounts matter.
Does this page look anything up online?
No. The MD5 runs in your browser, no input data ever leaves the page, and the tool keeps working with the network off. A genuine Mojang account UUID cannot be derived from a name at all, so for that use the UUID Lookup tool instead.