diff --git a/pandalib-paper-reflect/src/main/java/fr/pandacube/lib/paper/reflect/util/PrimaryWorlds.java b/pandalib-paper-reflect/src/main/java/fr/pandacube/lib/paper/reflect/util/PrimaryWorlds.java
new file mode 100644
index 0000000..978e886
--- /dev/null
+++ b/pandalib-paper-reflect/src/main/java/fr/pandacube/lib/paper/reflect/util/PrimaryWorlds.java
@@ -0,0 +1,40 @@
+package fr.pandacube.lib.paper.reflect.util;
+
+import fr.pandacube.lib.paper.reflect.wrapper.craftbukkit.CraftServer;
+import fr.pandacube.lib.reflect.wrapper.ReflectWrapper;
+import org.bukkit.Bukkit;
+import org.bukkit.plugin.Plugin;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * Utility method to get the list of the primary world of the Bukkit/Paper server.
+ * The primary worlds are the world that are loaded by the server at the startup, that the plugins cannot unload.
+ */
+public class PrimaryWorlds {
+
+	/**
+	 * An unmodifiable list containing the names of the primary worlds of this server instance, in the order they are
+	 * loaded. This list can be accessed even if the corresponding worlds are not yet loaded, for instance in the
+	 * {@link Plugin#onLoad()} method.
+	 */
+	public static final List<String> PRIMARY_WORLDS;
+
+
+	static {
+		List<String> primaryWorlds = new ArrayList<>(3);
+
+		String world = ReflectWrapper.wrapTyped(Bukkit.getServer(), CraftServer.class).getServer().getLevelIdName();
+
+		primaryWorlds.add(world);
+		if (Bukkit.getAllowNether()) primaryWorlds.add(world + "_nether");
+		if (Bukkit.getAllowEnd()) primaryWorlds.add(world + "_the_end");
+
+		PRIMARY_WORLDS = Collections.unmodifiableList(primaryWorlds);
+	}
+	
+
+	
+}
diff --git a/pandalib-paper/src/main/java/fr/pandacube/lib/paper/util/WorldUtil.java b/pandalib-paper/src/main/java/fr/pandacube/lib/paper/util/WorldUtil.java
new file mode 100644
index 0000000..84bc954
--- /dev/null
+++ b/pandalib-paper/src/main/java/fr/pandacube/lib/paper/util/WorldUtil.java
@@ -0,0 +1,75 @@
+package fr.pandacube.lib.paper.util;
+
+import org.bukkit.Bukkit;
+import org.bukkit.World.Environment;
+
+import java.io.File;
+import java.util.Arrays;
+import java.util.List;
+import java.util.regex.Pattern;
+
+public class WorldUtil {
+	
+	
+	
+	
+	public static Environment determineEnvironment(String world) {
+		if (Bukkit.getWorld(world) != null) {
+			return Bukkit.getWorld(world).getEnvironment();
+		}
+		
+		File worldFolder = worldDir(world);
+		
+		if (!worldFolder.isDirectory())
+			throw new IllegalStateException("The world " + world + " is not a valid world (directory not found).");
+		
+		if (!new File(worldFolder, "level.dat").isFile())
+			throw new IllegalStateException("The world " + world + " is not a valid world (level.dat not found).");
+		
+		if (new File(worldFolder, "region").isDirectory())
+			return Environment.NORMAL;
+		
+		if (new File(worldFolder, "DIM-1" + File.pathSeparator + "region").isDirectory())
+			return Environment.NETHER;
+		
+		if (new File(worldFolder, "DIM1" + File.pathSeparator + "region").isDirectory())
+			return Environment.THE_END;
+		
+		throw new IllegalStateException("Unable to determine the type of the world " + world + ".");
+	}
+	
+	
+	
+	private static final List<String> REGION_DATA_FILES = Arrays.asList("entities", "poi", "region", "DIM-1", "DIM1");
+	
+	public static List<File> regionDataFiles(String world) {
+		return onlyExistents(worldDir(world), REGION_DATA_FILES);
+	}
+
+	public static List<File> mapFiles(String world) {
+		Pattern mapFilePattern = Pattern.compile("map_\\d+.dat");
+		return List.of(dataDir(world).listFiles((dir, name) -> mapFilePattern.matcher(name).find() || "idcounts.dat".equals(name)));
+	}
+	
+	private static List<File> onlyExistents(File worldDir, List<String> searchList) {
+		return searchList.stream()
+				.map(f -> new File(worldDir, f))
+				.filter(File::exists)
+				.toList();
+	}
+
+	public static File worldDir(String world) {
+		return new File(Bukkit.getWorldContainer(), world);
+	}
+
+	public static File dataDir(String world) {
+		return new File(worldDir(world), "data");
+	}
+	
+	public static boolean isValidWorld(String world) {
+		File d = worldDir(world);
+		return d.isDirectory() && new File(d, "level.dat").isFile(); 
+	}
+	
+	
+}