# UUIDs

"UUID" stands for "Universally Unique Identifier". You can think of it as a serial number per Minecraft account.

When saving data long-term (anything you want to last over a restart or re-log), you should always use UUIDs as a key. This is because a player's username can change, but a UUID will not.

Here's an example with a variable:

If you were using `{example::%player%}` and someone had a Minecraft account with the username "Notch", and then joined your server and played, their data would be saved in `{example::Notch}`. 

However, if they change their username to "Herobrine" and then rejoin the server, Skript will now save data in and retrieve data from `{example::Herobrine}`. This means that they will lose (be unable to access) any and all of their old data.

If you instead used `%player's UUID%`, which is specific per Minecraft account, this would not be an issue, as the UUID does not change unless someone is on a completely different Minecraft account. This means that they will always be accessing `{example::314159265}`, and their data will persist.

{% hint style="info" %}
Skript is making a change to always use UUIDs when you use `%player%`, and if you want their username you must use `%player's name%`. Click [here](https://github.com/SkriptLang/Skript/discussions/6270) for more details about the change.
{% endhint %}


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