diff --git a/pandalib-paper/src/main/java/fr/pandacube/lib/paper/players/PaperOffPlayer.java b/pandalib-paper/src/main/java/fr/pandacube/lib/paper/players/PaperOffPlayer.java
index 53b9324..4e02f0f 100644
--- a/pandalib-paper/src/main/java/fr/pandacube/lib/paper/players/PaperOffPlayer.java
+++ b/pandalib-paper/src/main/java/fr/pandacube/lib/paper/players/PaperOffPlayer.java
@@ -1,9 +1,13 @@
 package fr.pandacube.lib.paper.players;
 
+import com.google.common.io.Files;
+import fr.pandacube.lib.paper.reflect.util.PrimaryWorlds;
 import fr.pandacube.lib.paper.reflect.wrapper.craftbukkit.CraftItemStack;
 import fr.pandacube.lib.paper.reflect.wrapper.craftbukkit.CraftServer;
 import fr.pandacube.lib.paper.reflect.wrapper.minecraft.nbt.CompoundTag;
 import fr.pandacube.lib.paper.reflect.wrapper.minecraft.nbt.ListTag;
+import fr.pandacube.lib.paper.reflect.wrapper.minecraft.nbt.NbtIo;
+import fr.pandacube.lib.paper.util.WorldUtil;
 import fr.pandacube.lib.players.standalone.AbstractOffPlayer;
 import fr.pandacube.lib.reflect.wrapper.ReflectWrapper;
 import org.bukkit.Bukkit;
@@ -13,6 +17,8 @@ import org.bukkit.event.inventory.InventoryType;
 import org.bukkit.inventory.ItemStack;
 import org.bukkit.scoreboard.Team;
 
+import java.io.File;
+import java.io.IOException;
 import java.util.function.UnaryOperator;
 
 /**
@@ -142,7 +148,15 @@ public interface PaperOffPlayer extends AbstractOffPlayer {
      * Player data
      */
 
+    /**
+     * Gets the NBT data from the playerdata file.
+     * It will not work if the player is online, because the data on the file are not synchronized with real-time values.
+     * @return the NBT data from the playerdata file.
+     * @throws IllegalStateException if the player is online.
+     */
     default CompoundTag getPlayerData() {
+        if (isOnline())
+            throw new IllegalStateException("Cannot access data file of " + getName() + " because they’re online.");
         return ReflectWrapper.wrapTyped(Bukkit.getServer(), CraftServer.class)
                 .getServer()
                 .getPlayerList()
@@ -150,6 +164,37 @@ public interface PaperOffPlayer extends AbstractOffPlayer {
                 .getPlayerData(getUniqueId().toString());
     }
 
+    /**
+     * Saves the provided NBT data to the playerdata file.
+     * It will not work if the player is online, because the provided data will be lost when the player disconnects.
+     * @param data the data to save.
+     * @throws IllegalStateException if the player is online.
+     * @throws IOException if an IO error occurs.
+     */
+    default void savePlayerData(CompoundTag data) throws IOException {
+        if (isOnline())
+            throw new IllegalStateException("Cannot write data file of " + getName() + " because they’re online.");
+        File file = getPlayerDataFile(false);
+        File old = getPlayerDataFile(true);
+        old.delete();
+        Files.move(file, old);
+        NbtIo.writeCompressed(data, file);
+    }
+
+    /**
+     * Gets the file where the playerdata is stored.
+     * @param old true to return the path of old data, false to return the actual file.
+     * @return the file where the playerdata is stored.
+     */
+    default File getPlayerDataFile(boolean old) {
+        File playerDataDir = new File(WorldUtil.worldDir(PrimaryWorlds.PRIMARY_WORLDS.get(0)), "playerdata");
+        return new File(playerDataDir, getUniqueId() + (old ? ".dat_old" : ".dat"));
+    }
+
+    /**
+     * Gets the content of the player’s inventory.
+     * @return the content of the player’s inventory.
+     */
     default ItemStack[] getInventoryContent() {
         ItemStack[] content = new ItemStack[InventoryType.PLAYER.getDefaultSize()];
         CompoundTag playerData = getPlayerData();
@@ -179,6 +224,10 @@ public interface PaperOffPlayer extends AbstractOffPlayer {
         return content;
     }
 
+    /**
+     * Gets the content of the player’s enderchest.
+     * @return the content of the player’s enderchest.
+     */
     default ItemStack[] getEnderchestContent() {
         ItemStack[] content = new ItemStack[InventoryType.ENDER_CHEST.getDefaultSize()];
         CompoundTag playerData = getPlayerData();