diff --git a/build.gradle.kts b/build.gradle.kts
index 866286e..9c4cf50 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -85,13 +85,12 @@ tasks.javadoc {
     options {
         (this as? StandardJavadocDocletOptions)?.apply {
             links(
-                "https://docs.oracle.com/javase/8/docs/api/",
+                "https://docs.oracle.com/en/java/javase/16/docs/api/",
                 "https://javadoc.io/doc/com.flowpowered/flow-math/1.0.3/",
                 "https://javadoc.io/doc/com.google.code.gson/gson/2.8.0/",
             )
             addStringOption("Xdoclint:none", "-quiet")
-            if (JavaVersion.current().isJava9Compatible)
-                addBooleanOption("html5", true)
+            addBooleanOption("html5", true)
         }
     }
 }
diff --git a/src/main/java/de/bluecolored/bluemap/api/AssetStorage.java b/src/main/java/de/bluecolored/bluemap/api/AssetStorage.java
index a5ba4a4..fe71137 100644
--- a/src/main/java/de/bluecolored/bluemap/api/AssetStorage.java
+++ b/src/main/java/de/bluecolored/bluemap/api/AssetStorage.java
@@ -35,6 +35,7 @@ import java.util.Optional;
 /**
  * A storage that is able to hold any "asset"-data for a map. For example images, icons, scripts or json-files.
  */
+@SuppressWarnings("unused")
 public interface AssetStorage {
 
     /**
diff --git a/src/main/java/de/bluecolored/bluemap/api/BlueMapAPI.java b/src/main/java/de/bluecolored/bluemap/api/BlueMapAPI.java
index 3fdffc3..b90b223 100644
--- a/src/main/java/de/bluecolored/bluemap/api/BlueMapAPI.java
+++ b/src/main/java/de/bluecolored/bluemap/api/BlueMapAPI.java
@@ -28,6 +28,7 @@ import com.google.gson.Gson;
 import com.google.gson.JsonElement;
 import com.google.gson.JsonObject;
 import de.bluecolored.bluemap.api.plugin.Plugin;
+import org.jetbrains.annotations.ApiStatus;
 
 import java.io.InputStream;
 import java.io.InputStreamReader;
@@ -42,6 +43,7 @@ import java.util.function.Consumer;
  * An API to control the running instance of BlueMap.
  * <p>This API is thread-save, so you <b>can</b> use it async, off the main-server-thread, to save performance!</p>
  */
+@SuppressWarnings({"unused", "UnusedReturnValue"})
 public abstract class BlueMapAPI {
 
     @SuppressWarnings("unused")
@@ -57,6 +59,7 @@ public abstract class BlueMapAPI {
                 gitHash = element.get("git-hash").getAsString();
             } catch (Exception ex) {
                 System.err.println("Failed to load version from resources!");
+                //noinspection CallToPrintStackTrace
                 ex.printStackTrace();
             }
         }
@@ -191,39 +194,33 @@ public abstract class BlueMapAPI {
      * @return <code>true</code> if the instance has been registered, <code>false</code> if there already was an instance registered
      * @throws ExecutionException if a listener threw an exception during the registration
      */
-    protected static synchronized boolean registerInstance(BlueMapAPI instance) throws ExecutionException {
+    @ApiStatus.Internal
+    protected static synchronized boolean registerInstance(BlueMapAPI instance) throws Exception {
         if (BlueMapAPI.instance != null) return false;
 
         BlueMapAPI.instance = instance;
 
-        List<Throwable> thrownExceptions = new ArrayList<>(0);
+        List<Exception> thrownExceptions = new ArrayList<>(0);
 
         for (Consumer<BlueMapAPI> listener : BlueMapAPI.onEnableConsumers) {
             try {
                 listener.accept(BlueMapAPI.instance);
-            } catch (Throwable ex) {
+            } catch (Exception ex) {
                 thrownExceptions.add(ex);
             }
         }
 
-        if (!thrownExceptions.isEmpty()) {
-            ExecutionException ex = new ExecutionException(thrownExceptions.get(0));
-            for (int i = 1; i < thrownExceptions.size(); i++) {
-                ex.addSuppressed(thrownExceptions.get(i));
-            }
-            throw ex;
-        }
-
-        return true;
+        return throwAsOne(thrownExceptions);
     }
 
     /**
      * Used by BlueMap to unregister the API and call the listeners properly.
      * @param instance the {@link BlueMapAPI} instance
-     * @return <code>true</code> if the instance was unregistered, <code>false</code> if there was no or an other instance registered
+     * @return <code>true</code> if the instance was unregistered, <code>false</code> if there was no or another instance registered
      * @throws ExecutionException if a listener threw an exception during the un-registration
      */
-    protected static synchronized boolean unregisterInstance(BlueMapAPI instance) throws ExecutionException {
+    @ApiStatus.Internal
+    protected static synchronized boolean unregisterInstance(BlueMapAPI instance) throws Exception {
         if (BlueMapAPI.instance != instance) return false;
 
         List<Exception> thrownExceptions = new ArrayList<>(0);
@@ -238,8 +235,12 @@ public abstract class BlueMapAPI {
 
         BlueMapAPI.instance = null;
 
+        return throwAsOne(thrownExceptions);
+    }
+
+    private static boolean throwAsOne(List<Exception> thrownExceptions) throws Exception {
         if (!thrownExceptions.isEmpty()) {
-            ExecutionException ex = new ExecutionException(thrownExceptions.get(0));
+            Exception ex = thrownExceptions.get(0);
             for (int i = 1; i < thrownExceptions.size(); i++) {
                 ex.addSuppressed(thrownExceptions.get(i));
             }
diff --git a/src/main/java/de/bluecolored/bluemap/api/BlueMapMap.java b/src/main/java/de/bluecolored/bluemap/api/BlueMapMap.java
index 7fbff94..8b22c86 100644
--- a/src/main/java/de/bluecolored/bluemap/api/BlueMapMap.java
+++ b/src/main/java/de/bluecolored/bluemap/api/BlueMapMap.java
@@ -28,6 +28,7 @@ import com.flowpowered.math.vector.Vector2i;
 import com.flowpowered.math.vector.Vector3d;
 import com.flowpowered.math.vector.Vector3i;
 import de.bluecolored.bluemap.api.markers.MarkerSet;
+import org.jetbrains.annotations.ApiStatus;
 
 import java.util.Map;
 import java.util.function.Predicate;
@@ -36,6 +37,7 @@ import java.util.function.Predicate;
  * This class represents a map that is rendered by BlueMap of a specific world ({@link BlueMapWorld}).
  * Each map belongs to a map configured in BlueMap's configuration file (in the <code>maps: []</code> list).
  */
+@SuppressWarnings("unused")
 public interface BlueMapMap {
 
     /**
@@ -91,6 +93,7 @@ public interface BlueMapMap {
      * <p>Any previously set filters will get overwritten with the new one. You can get the current filter using {@link #getTileFilter()} and combine them if you wish.</p>
      * @param filter The filter that will be used from now on.
      */
+    @ApiStatus.Experimental
     void setTileFilter(Predicate<Vector2i> filter);
 
     /**
@@ -109,6 +112,7 @@ public interface BlueMapMap {
     /**
      * Returns the currently set TileFilter. The default TileFilter is equivalent to <code>t -&gt; true</code>.
      */
+    @ApiStatus.Experimental
     Predicate<Vector2i> getTileFilter();
 
     /**
diff --git a/src/main/java/de/bluecolored/bluemap/api/RenderManager.java b/src/main/java/de/bluecolored/bluemap/api/RenderManager.java
index fb8f6e1..9a0fc6c 100644
--- a/src/main/java/de/bluecolored/bluemap/api/RenderManager.java
+++ b/src/main/java/de/bluecolored/bluemap/api/RenderManager.java
@@ -26,12 +26,12 @@ package de.bluecolored.bluemap.api;
 
 import com.flowpowered.math.vector.Vector2i;
 
-import java.io.IOException;
 import java.util.Collection;
 
 /**
  * The {@link RenderManager} is used to schedule tile-renders and process them on a number of different threads.
  */
+@SuppressWarnings("unused")
 public interface RenderManager {
 
     /**
@@ -66,9 +66,8 @@ public interface RenderManager {
      * An update-task will be scheduled right after the purge, to get the map up-to-date again.
      * @param map the map to be purged
      * @return true if a new task has been scheduled, false if not (usually because there is already an update-task for this map scheduled)
-     * @throws IOException if an IOException occurs while trying to create the task.
      */
-    boolean scheduleMapPurgeTask(BlueMapMap map) throws IOException;
+    boolean scheduleMapPurgeTask(BlueMapMap map);
 
     /**
      * Getter for the current size of the render-queue.
diff --git a/src/main/java/de/bluecolored/bluemap/api/WebApp.java b/src/main/java/de/bluecolored/bluemap/api/WebApp.java
index f0ee1f6..e2ad2b6 100644
--- a/src/main/java/de/bluecolored/bluemap/api/WebApp.java
+++ b/src/main/java/de/bluecolored/bluemap/api/WebApp.java
@@ -24,6 +24,8 @@
  */
 package de.bluecolored.bluemap.api;
 
+import org.jetbrains.annotations.ApiStatus;
+
 import java.awt.image.BufferedImage;
 import java.io.IOException;
 import java.nio.file.Path;
@@ -31,6 +33,7 @@ import java.util.Map;
 import java.util.UUID;
 import java.util.function.Consumer;
 
+@SuppressWarnings("unused")
 public interface WebApp {
 
     /**
@@ -44,6 +47,7 @@ public interface WebApp {
      * @param player the UUID of the player
      * @param visible true if the player-marker should be visible, false if it should be hidden
      */
+    @ApiStatus.Experimental
     void setPlayerVisibility(UUID player, boolean visible);
 
     /**
@@ -51,6 +55,7 @@ public interface WebApp {
      * @see #setPlayerVisibility(UUID, boolean)
      * @param player the UUID of the player
      */
+    @ApiStatus.Experimental
     boolean getPlayerVisibility(UUID player);
 
     /**
diff --git a/src/main/java/de/bluecolored/bluemap/api/gson/MarkerGson.java b/src/main/java/de/bluecolored/bluemap/api/gson/MarkerGson.java
index de973a9..d113999 100644
--- a/src/main/java/de/bluecolored/bluemap/api/gson/MarkerGson.java
+++ b/src/main/java/de/bluecolored/bluemap/api/gson/MarkerGson.java
@@ -49,8 +49,9 @@ public final class MarkerGson {
             .setLenient()
             .create();
 
-    /* This class can not be instantiated. */
-    private MarkerGson() {}
+    private MarkerGson() {
+        throw new UnsupportedOperationException("Utility class");
+    }
 
     public static GsonBuilder addAdapters(GsonBuilder builder) {
         return builder
diff --git a/src/main/java/de/bluecolored/bluemap/api/plugin/Plugin.java b/src/main/java/de/bluecolored/bluemap/api/plugin/Plugin.java
index 05f737f..d73e211 100644
--- a/src/main/java/de/bluecolored/bluemap/api/plugin/Plugin.java
+++ b/src/main/java/de/bluecolored/bluemap/api/plugin/Plugin.java
@@ -24,6 +24,7 @@
  */
 package de.bluecolored.bluemap.api.plugin;
 
+@SuppressWarnings("unused")
 public interface Plugin {
 
     /**