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What a Minecraft UUID is—and which players this guide covers
A UUID (universally unique identifier) is the 128-bit identifier Minecraft uses to distinguish players. A Java server uses it for player data and access-control lists rather than treating the displayed username as the permanent key. That distinction matters after a username change: an online-mode Java account keeps its UUID, while a server’s whitelist or ban record can continue to identify the same account even when the name label changes.
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This guide targets Java Edition servers and their administrators. Bedrock players who connect through Geyser or Floodgate have a separate format noted below. The exact files described are on the machine running the Java server, not in a player’s ordinary client installation.
Choose the lookup method that fits the situation
| Method | Must the player have joined? | Works for an unseen player? | External endpoint or site | Best use |
|---|---|---|---|---|
usercache.json |
Yes, the server must have cached the player | No | None | First check for a name-to-UUID answer |
world/playerdata/<uuid>.dat filenames |
Yes, the player must have data in that world | No | None | Confirm that a player actually has world data |
whitelist.json or banned-players.json |
Usually; an administrator may have added a player before a first join | Potentially, if an entry was added in advance | None | Find the UUID attached to an access or ban entry |
| Mojang profile lookup | No | Yes, if the service returns a profile | Yes; the current URL and method require caution | Look up a name absent from local files |
| Third-party lookup services | Depends on their collected history | Sometimes | Yes | Optional convenience or name-history context; accuracy is not established here |
Use the local files in order. They avoid an external dependency and show what this particular server has actually seen. Only move to an online lookup when the player is not represented locally.
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Method 1: read usercache.json
Find the file in the server root
usercache.json is in the server’s root directory—the folder containing the server JAR and the world folders. It is not normally inside world/. If the server is managed by a hosting panel, open the panel’s file manager and go to the instance’s top-level directory. On a self-hosted machine, open the directory from which the server was launched (or the directory supplied as the server’s working directory).
Stop the server, or at least avoid editing files while it is writing them. Make a backup before changing any JSON. To look up a UUID, you only need to read the file; do not alter it.
Read the name and UUID pair
Open the file in a text editor that displays JSON. Its entries contain a player’s name and UUID, along with cache metadata. Search for the exact username as it appears in the entry. The UUID value beside that name is the identifier to use for Java server administration.
[
{
"name": "ExamplePlayer",
"uuid": "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx",
"expiresOn": "..."
}
]The illustration shows the relevant fields only; your file’s metadata and ordering can differ. The cache’s retention period is not specified, so do not infer a fixed expiry period from an old or missing entry. If the name is absent, check the world data and access lists before assuming the player never connected.
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On a system with jq, this prints every cached name and UUID:
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jq -r '.[] | [.name, .uuid] | @tsv' usercache.jsonTo filter one name (case handling depends on your shell and the JSON content), first print the list and search the output. On Windows PowerShell, the equivalent structured read is:
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Select-Object name, uuidThese commands read the file only. They do not contact Mojang and cannot produce a result for a player who is not in the cache.
Method 2: infer the UUID from world/playerdata
Use the filename, not the contents
Go to the active world’s playerdata directory. In a default setup the path is:
world/playerdata/Each player data file is named <uuid>.dat. The filename itself reveals the UUID, including the dashed form. This is useful when you know a player’s files exist but the cache entry is difficult to find.
- Identify the world the server is currently using; it may not be named
worldif thelevel-namesetting was changed. - Open that world’s
playerdatafolder. - Copy the UUID portion of a
.datfilename, removing only the.datsuffix. - Match that UUID to a name in
usercache.json,whitelist.json, orbanned-players.jsonwhen you need to identify which player owns an otherwise anonymous file.
A file proves that player data exists for that world; it does not, by itself, contain a readable username in the filename. If several worlds are present, searching the wrong world’s folder can make a known player appear to be missing.
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Do not confuse other UUID-named folders
Server plugins and dimensions can create additional UUID-based files. For the vanilla player identity, use the active world’s playerdata path. Keep the complete UUID and its hyphens when copying it into an access list.
Method 3: inspect whitelist and ban files
whitelist.json
The server whitelist is a JSON array whose entries have two important fields: uuid and name. The UUID is the key the server checks; name is a human-readable label. A stale name does not necessarily mean the UUID is wrong, especially after a rename.
[
{
"uuid": "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx",
"name": "ExamplePlayer"
}
]To find a player’s UUID, search for the name and copy the value of uuid. If you are diagnosing a “whitelist UUID not working” error, validate the value’s format and verify that the entry is in the whitelist file for the server instance you actually started.
banned-players.json
The banned-player list also pairs UUIDs with names. Search it when the question is tied to a ban, an appeal, or a command-generated entry. As with the whitelist, use the UUID field as the identity and treat the name as a label.
Reload safely after an intentional edit
Do not manually edit these files while the server is running unless you understand how your server manager reloads them; a later save can overwrite your change. Prefer the server’s whitelist or ban commands, then check the resulting JSON to confirm the dashed UUID was written. Make a backup before any manual repair.
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UUID formatting: dashed versus undashed
Java access-list files expect the conventional dashed form:
xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxxThe groups are 8-4-4-4-12 hexadecimal characters. Some Mojang API responses use a trimmed 32-character value with no hyphens. If you receive that form, insert hyphens after characters 8, 12, 16, and 20 before placing it in whitelist.json or another file that expects the conventional representation. Do not add spaces, braces, or quotation marks inside the UUID value.
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- Exactly 36 characters including four hyphens.
- Hyphens at positions 9, 14, 19, and 24 (counting from 1).
- Only hexadecimal characters (0-9 and a-f, case-insensitive) in the other positions.
- The copied value matches the same account’s local record, rather than a similarly named player.
Finding a UUID for a player who has never joined
A new player will not be in your server’s usercache.json or world playerdata. An administrator can still need a UUID to pre-populate a whitelist, so a Mojang profile lookup is the remaining first-party route. As of 14 October 2026, the available guides disagree about the endpoint and request method; none of the alternatives below should be presented as a guaranteed current API contract without checking Mojang’s own documentation and testing the response.
Endpoint variants reported by current guides
- A per-name GET is described as
https://api.mojang.com/users/profiles/minecraft/<username>. - A bulk POST (up to 10 names) is described as
https://api.minecraftservices.com/minecraft/profile/lookup/bulk/byname. - The Minecraft Wiki’s user-cache description gives a POST to
https://api.mojang.com/profiles/minecraft.
Because these instructions conflict, avoid hard-coding one URL into an automated whitelist workflow without verifying it first. If a request succeeds, inspect the returned profile’s name and UUID, convert an undashed UUID to the dashed 8-4-4-4-12 form, and then confirm the result against the server’s own records after the player joins.
Interpret an unsuccessful response correctly
- A “not found” result can mean the name is misspelled, the account has no matching Java profile, or the endpoint behavior has changed.
- An HTTP or authentication error may indicate that the chosen method is no longer supported, not that the player has no UUID.
- Never substitute an offline-mode UUID for an online-mode account merely because the online lookup failed; the algorithms and identifiers are different.
Offline-mode servers: why the UUID is different
When a server runs in offline mode, it does not verify a player’s Mojang account with the authentication service. Instead, the UUID is generated from an MD5 hash of the string OfflinePlayer: followed by the username. The resulting identifier is a version 3 UUID, so its third group starts with 3.
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This has two operational consequences:
- The same username on two unrelated offline-mode servers is not a Mojang account identity; each server derives its own local identity.
- Renaming an offline-mode player changes the input string and therefore changes the UUID. Existing whitelist, ban, inventory, and player-data entries can stop matching the renamed account.
For an offline server, trust the UUID already present in that server’s files. Do not paste an online-mode UUID from a profile service into an offline-mode whitelist unless you have deliberately migrated the player’s data and understand the consequences.
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Bedrock players connecting through Geyser or Floodgate
Bedrock users do not normally have Java account UUIDs. When they connect to a Java server through Geyser/Floodgate, reported UUIDs commonly begin with:
00000000-0000-0000-Treat that prefix as a diagnostic clue, not as a replacement for checking the server’s own files. Search usercache.json, access lists, and the relevant world data for the exact entry created by the bridge. A Bedrock username, Java username, and UUID may not line up the way they do for a native Java connection, so copy the UUID associated with the bridge-created record rather than calculating one from the visible name.
Troubleshooting common lookup failures
| Symptom | Likely cause | What to check |
|---|---|---|
The name is absent from usercache.json |
The player has not joined this server, the cache entry is no longer present, or you opened the wrong instance | Confirm the server root, inspect the active world’s playerdata, then check access lists |
No .dat file appears |
You searched a different world, or the player has no data in that world | Check the configured world name and every relevant world directory |
| Whitelist rejects a UUID | Undashed API output, a typo, wrong account, or an entry edited while the server was running | Use the 8-4-4-4-12 form, compare with local records, back up, and reload through server controls |
| Name in the whitelist looks old | The name field is only a label and may predate a rename | Use the UUID as the identity; verify it against current player data |
| Offline player lost access after renaming | Offline UUIDs are derived from the username, so the UUID changed | Locate the old UUID’s files and perform a deliberate data/access migration |
| Bedrock player has an unexpected UUID | Geyser/Floodgate is supplying a bridge-specific identity | Copy the UUID from the bridge-created local entry, often recognizable by the reported zero prefix |
| Profile API returns an error | The endpoint or method in an older guide may no longer be valid | Do not guess a replacement; verify the current Mojang documentation and use local records once the player joins |
A safe, repeatable administrator workflow
- Identify the server instance. Confirm the root directory and the world named in the server configuration; panels often host multiple instances.
- Back up before editing. Copy
usercache.json, the relevant access lists, and the world folder to a safe location. - Search local identity records. Check
usercache.json, thenworld/playerdata, thenwhitelist.jsonandbanned-players.json. - Normalize the format. Keep a dashed 8-4-4-4-12 UUID for whitelist and ban files; convert only the presentation, not the hexadecimal value.
- Classify the server. Determine whether it is online mode, offline mode, or accepting Bedrock connections through Geyser/Floodgate. This decides which UUID family is meaningful.
- Use an external lookup only for an unseen Java player. Treat the conflicting Mojang endpoint descriptions as unverified until tested against current official documentation.
- Validate after connection. Once the player joins, confirm that the new or updated entry in the server files matches the UUID you recorded before granting access or moving data.
What to record for future administration
For each player, keep the UUID, the exact name observed by the server, the server mode, and (when relevant) whether the connection came through Geyser/Floodgate. Recording the source—such as usercache.json or a specific world’s playerdata filename—makes later audits easier and helps distinguish an online account from an offline-mode or bridged identity. Do not rely on a username alone for permissions, bans, inventories, or migrations.
Bottom line
On a Java server, the quickest reliable answer is local: read usercache.json, then confirm with the active world’s UUID-named player-data file or an access-list entry. Preserve the dashed UUID format expected by whitelist files. Reserve Mojang profile lookups for players who have never joined, and treat the currently conflicting endpoint instructions as unverified. Offline mode and Bedrock bridges use different identity rules, so classify the connection before changing a player’s permissions or data.
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