Mix of Checkstyle and SonarLint.

api/src/ap/java/com/velocitypowered/api/plugin/ap/PluginAnnotationProcessor.java

@@ -2,7 +2,6 @@ package com.velocitypowered.api.plugin.ap;
 
 import com.google.gson.Gson;
 import com.velocitypowered.api.plugin.Plugin;
-import com.velocitypowered.api.plugin.PluginDescription;
 import java.io.BufferedWriter;
 import java.io.IOException;
 import java.io.Writer;
@@ -66,7 +65,7 @@ public class PluginAnnotationProcessor extends AbstractProcessor {
       }
 
       Plugin plugin = element.getAnnotation(Plugin.class);
-      if (!PluginDescription.ID_PATTERN.matcher(plugin.id()).matches()) {
+      if (!SerializedPluginDescription.ID_PATTERN.matcher(plugin.id()).matches()) {
         environment.getMessager().printMessage(Diagnostic.Kind.ERROR, "Invalid ID for plugin "
             + qualifiedName
             + ". IDs must start alphabetically, have alphanumeric characters, and can "

api/src/ap/java/com/velocitypowered/api/plugin/ap/SerializedPluginDescription.java

@@ -8,11 +8,14 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Objects;
+import java.util.regex.Pattern;
 import java.util.stream.Collectors;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
 public class SerializedPluginDescription {
 
+  public static final Pattern ID_PATTERN = Pattern.compile("[a-z][a-z0-9-_]{0,63}");
+
   // @Nullable is used here to make GSON skip these in the serialized file
   private final String id;
   private final @Nullable String name;
@@ -26,7 +29,9 @@ public class SerializedPluginDescription {
   private SerializedPluginDescription(String id, String name, String version, String description,
       String url,
       List<String> authors, List<Dependency> dependencies, String main) {
-    this.id = Preconditions.checkNotNull(id, "id");
+    Preconditions.checkNotNull(id, "id");
+    Preconditions.checkArgument(ID_PATTERN.matcher(id).matches(), "id is not valid");
+    this.id = id;
     this.name = Strings.emptyToNull(name);
     this.version = Strings.emptyToNull(version);
     this.description = Strings.emptyToNull(description);

api/src/main/java/com/velocitypowered/api/event/connection/ConnectionHandshakeEvent.java

@@ -4,7 +4,7 @@ import com.google.common.base.Preconditions;
 import com.velocitypowered.api.proxy.InboundConnection;
 
 /**
- * This event is fired when a handshake is established between a client and Velocity.
+ * This event is fired when a handshake is established between a client and the proxy.
  */
 public final class ConnectionHandshakeEvent {
 

api/src/main/java/com/velocitypowered/api/plugin/Plugin.java

@@ -14,7 +14,8 @@ public @interface Plugin {
 
   /**
    * The ID of the plugin. This ID should be unique as to not conflict with other plugins. The
-   * plugin ID must match the {@link PluginDescription#ID_PATTERN}.
+   * plugin ID may contain alphanumeric characters, dashes, and underscores, and be a maximum
+   * of 64 characters long.
    *
    * @return the ID for this plugin
    */

api/src/main/java/com/velocitypowered/api/util/title/TextTitle.java

@@ -186,21 +186,23 @@ public final class TextTitle implements Title {
       return this;
     }
 
-    public Builder stay(int ticks) {
+    private int checkTicks(int ticks) {
       Preconditions.checkArgument(ticks >= 0, "ticks value %s is negative", ticks);
-      this.stay = ticks;
+      return ticks;
+    }
+
+    public Builder stay(int ticks) {
+      this.stay = checkTicks(ticks);
       return this;
     }
 
     public Builder fadeIn(int ticks) {
-      Preconditions.checkArgument(ticks >= 0, "ticks value %s is negative", ticks);
-      this.fadeIn = ticks;
+      this.fadeIn = checkTicks(ticks);
       return this;
     }
 
     public Builder fadeOut(int ticks) {
-      Preconditions.checkArgument(ticks >= 0, "ticks value %s is negative", ticks);
-      this.fadeOut = ticks;
+      this.fadeOut = checkTicks(ticks);
       return this;
     }