Minecraft Player UUID Generator

Understanding Minecraft UUIDs: How Player Identity Works

Prior to Minecraft release 1.7.6 in 2014, player accounts were identified purely by their in-game username. This caused critical problems whenever players wanted to change their usernames: all player inventories, advancements, permissions, whitelist entries, and bans were wiped out.

To resolve this, Mojang transitioned the entire Minecraft ecosystem to 128-bit Universally Unique Identifiers (UUIDs). Every player in both Minecraft Java Edition and Bedrock Edition is assigned a permanent UUID that acts as the immutable primary key for all world save data.

Online Mode vs. Offline Mode (Cracked / LAN) UUIDs

Minecraft servers handle player identity in two distinct ways depending on the online-mode setting in your server.properties file:

The Offline Player UUID Formula (RFC 4122 Version 3)

In offline mode (used widely in LAN parties, development testing, and private networks), the server cannot contact Mojang to retrieve the player's account UUID. Instead, it deterministically computes an RFC 4122 Version 3 UUID using the MD5 hash of the string prefix:

// Standard Java Edition Offline UUID Algorithm
String input = "OfflinePlayer:" + username;
byte[] hash = MessageDigest.getInstance("MD5").digest(input.getBytes(StandardCharsets.UTF_8));

// Set Version 3 (0x30)
hash[6] = (byte) ((hash[6] & 0x0f) | 0x30);
// Set Variant 1 (0x80)
hash[8] = (byte) ((hash[8] & 0x3f) | 0x80);

UUID offlineUuid = UUID.nameUUIDFromBytes(hash);

Because MD5 is deterministic, entering the same username will always generate the exact same offline UUID across any Paper, Spigot, Bukkit, or Fabric server worldwide.

Full Hyphenated vs Trimmed UUIDs

In the Minecraft technical ecosystem, UUIDs exist in two standard string representations:

• Full Hyphenated UUID (36 characters): Formatted with hyphens in the standard 8-4-4-4-12 pattern (e.g. c8e5be26-5b72-3580-b2a6-2007f30e6914). This format is required inside server files like whitelist.json, ops.json, banned-players.json, and plugin databases.
• Trimmed UUID (32 characters): Stripped of all hyphens (e.g. c8e5be265b723580b2a62007f30e6914). Mojang's official REST API endpoints exclusively accept trimmed UUIDs for skin lookups and profile queries.

Where Minecraft Servers Store Player Data

Server administrators managing Spigot, Paper, Bukkit, or Purpur servers often need player UUIDs to recover lost inventories or fix corrupted player profiles. Player data is stored across three main directories in the root world folder:

• world/playerdata/<UUID>.dat — Stores player inventory, Ender Chest contents, health, hunger, XP levels, and coordinates in GZIP-compressed NBT format.
• world/stats/<UUID>.json — Stores all player statistics (blocks mined, time played, deaths, mob kills).
• world/advancements/<UUID>.json — Tracks completed advancements and recipe unlocks.

Production Code: Generating Minecraft UUIDs Programmatically

// Java: Native Bukkit / Spigot / Paper implementation
import java.nio.charset.StandardCharsets;
import java.util.UUID;

public class MinecraftUUIDHelper {
    public static UUID getOfflinePlayerUUID(String username) {
        return UUID.nameUUIDFromBytes(("OfflinePlayer:" + username).getBytes(StandardCharsets.UTF_8));
    }

    public static String toTrimmed(UUID uuid) {
        return uuid.toString().replace("-", "");
    }
}

// Node.js: Generate Minecraft Offline UUID
import crypto from 'crypto';

function getMinecraftOfflineUUID(username) {
  const hash = crypto.createHash('md5').update('OfflinePlayer:' + username).digest();
  
  // Set version 3 (MD5) and variant 1
  hash[6] = (hash[6] & 0x0f) | 0x30;
  hash[8] = (hash[8] & 0x3f) | 0x80;

  const hex = hash.toString('hex');
  return `${hex.slice(0,8)}-${hex.slice(8,12)}-${hex.slice(12,16)}-${hex.slice(16,20)}-${hex.slice(20)}`;
}

console.log(getMinecraftOfflineUUID('Steve'));
// Output: c8e5be26-5b72-3580-b2a6-2007f30e6914

# Python 3: Minecraft Offline UUID Calculation
import hashlib
import uuid

def get_minecraft_offline_uuid(username: str) -> uuid.UUID:
    data = ("OfflinePlayer:" + username).encode('utf-8')
    md5_hash = bytearray(hashlib.md5(data).digest())
    
    # Set Version 3 (0x30) and Variant 1 (0x80)
    md5_hash[6] = (md5_hash[6] & 0x0f) | 0x30
    md5_hash[8] = (md5_hash[8] & 0x3f) | 0x80
    
    return uuid.UUID(bytes=bytes(md5_hash))

print(get_minecraft_offline_uuid("Steve"))
# Output: c8e5be26-5b72-3580-b2a6-2007f30e6914

# Bash: Query Mojang official API for Online UUID
curl -s "https://api.mojang.com/users/profiles/minecraft/Notch" | jq .

# Response:
# {
#   "name": "Notch",
#   "id": "069a79f444e94726a5befca90e38aaf5"
# }