diff --git a/commands-bukkit/src/main/java/com/intellectualsites/commands/BukkitCommandSender.java b/commands-bukkit/src/main/java/com/intellectualsites/commands/BukkitCommandSender.java
index 2268aede..c77b1ebd 100644
--- a/commands-bukkit/src/main/java/com/intellectualsites/commands/BukkitCommandSender.java
+++ b/commands-bukkit/src/main/java/com/intellectualsites/commands/BukkitCommandSender.java
@@ -82,4 +82,8 @@ public abstract class BukkitCommandSender implements CommandSender {
     @Nonnull
     public abstract Player asPlayer();
 
+    @Override
+    public boolean hasPermission(@Nonnull final String permission) {
+        return this.internalSender.hasPermission(permission);
+    }
 }
diff --git a/commands-core/src/main/java/com/intellectualsites/commands/Command.java b/commands-core/src/main/java/com/intellectualsites/commands/Command.java
index fc7cb869..6af472e4 100644
--- a/commands-core/src/main/java/com/intellectualsites/commands/Command.java
+++ b/commands-core/src/main/java/com/intellectualsites/commands/Command.java
@@ -144,7 +144,13 @@ public class Command<C extends CommandSender> {
     }
 
 
-    public static class Builder<C extends CommandSender> {
+    /**
+     * Builder for {@link Command} instances. The builder is immutable, and each
+     * setter method will return a new builder instance.
+     *
+     * @param <C> Command sender type
+     */
+    public static final class Builder<C extends CommandSender> {
 
         @Nonnull private final List<CommandComponent<C, ?>> commandComponents;
         @Nonnull private final CommandExecutionHandler<C> commandExecutionHandler;
@@ -155,10 +161,10 @@ public class Command<C extends CommandSender> {
                         @Nonnull final List<CommandComponent<C, ?>> commandComponents,
                         @Nonnull final CommandExecutionHandler<C> commandExecutionHandler,
                         @Nonnull final String commandPermission) {
-            this.commandComponents = commandComponents;
-            this.commandExecutionHandler = commandExecutionHandler;
             this.senderType = senderType;
-            this.commandPermission = commandPermission;
+            this.commandComponents = Objects.requireNonNull(commandComponents, "Components may not be null");
+            this.commandExecutionHandler = Objects.requireNonNull(commandExecutionHandler, "Execution handler may not be null");
+            this.commandPermission = Objects.requireNonNull(commandPermission, "Permission may not be null");
         }
 
         /**
diff --git a/commands-core/src/main/java/com/intellectualsites/commands/CommandManager.java b/commands-core/src/main/java/com/intellectualsites/commands/CommandManager.java
index 8ab9633a..3f00e4a6 100644
--- a/commands-core/src/main/java/com/intellectualsites/commands/CommandManager.java
+++ b/commands-core/src/main/java/com/intellectualsites/commands/CommandManager.java
@@ -59,11 +59,28 @@ public abstract class CommandManager<C extends CommandSender> {
         this.commandRegistrationHandler = commandRegistrationHandler;
     }
 
+    /**
+     * Execute a command and get a future that completes with the result
+     *
+     * @param commandSender Sender of the command
+     * @param input         Input provided by the sender
+     * @return Command result
+     */
+    @Nonnull
     public CompletableFuture<CommandResult> executeCommand(@Nonnull final C commandSender, @Nonnull final String input) {
         final CommandContext<C> context = new CommandContext<>(commandSender);
         return this.commandExecutionCoordinator.coordinateExecution(context, tokenize(input));
     }
 
+    /**
+     * Get command suggestions for the "next" argument that would yield a correctly
+     * parsing command input
+     *
+     * @param commandSender Sender of the command
+     * @param input         Input provided by the sender
+     * @return List of suggestions
+     */
+    @Nonnull
     public List<String> suggest(@Nonnull final C commandSender, @Nonnull final String input) {
         final CommandContext<C> context = new CommandContext<>(commandSender);
         return this.commandTree.getSuggestions(context, tokenize(input));
@@ -105,10 +122,15 @@ public abstract class CommandManager<C extends CommandSender> {
      *
      * @param commandSyntaxFormatter New formatter
      */
-    public void setCommandSyntaxFormatter(@Nonnull final CommandSyntaxFormatter commandSyntaxFormatter) {
+    public void setCommandSyntaxFormatter(@Nonnull final CommandSyntaxFormatter<C> commandSyntaxFormatter) {
         this.commandSyntaxFormatter = commandSyntaxFormatter;
     }
 
+    /**
+     * Get the command registration handler
+     *
+     * @return Command registration handler
+     */
     @Nonnull
     protected CommandRegistrationHandler getCommandRegistrationHandler() {
         return this.commandRegistrationHandler;
diff --git a/commands-core/src/main/java/com/intellectualsites/commands/CommandTree.java b/commands-core/src/main/java/com/intellectualsites/commands/CommandTree.java
index 91623893..53cf4858 100644
--- a/commands-core/src/main/java/com/intellectualsites/commands/CommandTree.java
+++ b/commands-core/src/main/java/com/intellectualsites/commands/CommandTree.java
@@ -130,7 +130,7 @@ public class CommandTree<C extends CommandSender> {
                             throw new InvalidSyntaxException(this.commandManager.getCommandSyntaxFormatter()
                                                                                 .apply(Objects.requireNonNull(child.getValue()
                                                                                                                    .getOwningCommand())
-                                                                                                                   .getComponents()),
+                                                                                              .getComponents()),
                                                              commandContext.getCommandSender(), this.getChain(root)
                                                                                                     .stream()
                                                                                                     .map(Node::getValue)
@@ -167,13 +167,12 @@ public class CommandTree<C extends CommandSender> {
                 throw new InvalidSyntaxException(this.commandManager.getCommandSyntaxFormatter()
                                                                     .apply(Objects.requireNonNull(
                                                                             Objects.requireNonNull(root.getValue())
-                                                                                                       .getOwningCommand())
-                                                                                                       .getComponents()),
+                                                                                   .getOwningCommand())
+                                                                                  .getComponents()),
                                                  commandContext.getCommandSender(), this.getChain(root)
                                                                                         .stream()
                                                                                         .map(Node::getValue)
-                                                                                        .collect(
-                                                                                                Collectors.toList()));
+                                                                                        .collect(Collectors.toList()));
             }
         } else {
             final Iterator<Node<CommandComponent<C, ?>>> childIterator = root.getChildren().iterator();
@@ -258,7 +257,8 @@ public class CommandTree<C extends CommandSender> {
                 if (component.getValue() == null || !this.isPermitted(commandContext.getCommandSender(), component)) {
                     continue;
                 }
-                suggestions.addAll(component.getValue().getParser().suggestions(commandContext, stringOrEmpty(commandQueue.peek())));
+                suggestions.addAll(
+                        component.getValue().getParser().suggestions(commandContext, stringOrEmpty(commandQueue.peek())));
             }
             return suggestions;
         }
@@ -410,6 +410,11 @@ public class CommandTree<C extends CommandSender> {
     }
 
 
+    /**
+     * Very simple tree structure
+     *
+     * @param <T> Node value type
+     */
     private static final class Node<T> {
 
         private final Map<String, String> nodeMeta = new HashMap<>();
diff --git a/commands-core/src/main/java/com/intellectualsites/commands/components/CommandComponent.java b/commands-core/src/main/java/com/intellectualsites/commands/components/CommandComponent.java
index 80de965f..a4463198 100644
--- a/commands-core/src/main/java/com/intellectualsites/commands/components/CommandComponent.java
+++ b/commands-core/src/main/java/com/intellectualsites/commands/components/CommandComponent.java
@@ -179,7 +179,13 @@ public class CommandComponent<C extends CommandSender, T> implements Comparable<
     }
 
 
-    public static class Builder<C extends CommandSender, T> {
+    /**
+     * Mutable builder for {@link CommandComponent} instances
+     *
+     * @param <C> Command sender type
+     * @param <T> Component value type
+     */
+    public static final class Builder<C extends CommandSender, T> {
 
         private String name;
         private boolean required = true;
diff --git a/commands-core/src/main/java/com/intellectualsites/commands/components/CommandSyntaxFormatter.java b/commands-core/src/main/java/com/intellectualsites/commands/components/CommandSyntaxFormatter.java
index d360a4a4..7a64e662 100644
--- a/commands-core/src/main/java/com/intellectualsites/commands/components/CommandSyntaxFormatter.java
+++ b/commands-core/src/main/java/com/intellectualsites/commands/components/CommandSyntaxFormatter.java
@@ -29,6 +29,11 @@ import javax.annotation.Nonnull;
 import java.util.List;
 import java.util.function.Function;
 
+/**
+ * Utility that formats chains of {@link CommandComponent command components} into syntax strings
+ *
+ * @param <C> Command sender type
+ */
 @FunctionalInterface
 public interface CommandSyntaxFormatter<C extends CommandSender> extends Function<List<CommandComponent<C, ?>>, String> {
 
diff --git a/commands-core/src/main/java/com/intellectualsites/commands/components/StandardCommandSyntaxFormatter.java b/commands-core/src/main/java/com/intellectualsites/commands/components/StandardCommandSyntaxFormatter.java
index cc930cd7..f677bb81 100644
--- a/commands-core/src/main/java/com/intellectualsites/commands/components/StandardCommandSyntaxFormatter.java
+++ b/commands-core/src/main/java/com/intellectualsites/commands/components/StandardCommandSyntaxFormatter.java
@@ -29,6 +29,16 @@ import javax.annotation.Nonnull;
 import java.util.Iterator;
 import java.util.List;
 
+/**
+ * {@link CommandSyntaxFormatter} implementation that uses the following rules:
+ * <ul>
+ *     <li>static components are serialized as their name, without a bracket</li>
+ *     <li>required components are serialized as their name, surrounded by angle brackets</li>
+ *     <li>optional components are serialized as their name, surrounded by square brackets</li>
+ * </ul>
+ *
+ * @param <C> Command sender type
+ */
 public class StandardCommandSyntaxFormatter<C extends CommandSender> implements CommandSyntaxFormatter<C> {
 
     public StandardCommandSyntaxFormatter() {
diff --git a/commands-core/src/main/java/com/intellectualsites/commands/components/StaticComponent.java b/commands-core/src/main/java/com/intellectualsites/commands/components/StaticComponent.java
index 3a1238d8..1d835986 100644
--- a/commands-core/src/main/java/com/intellectualsites/commands/components/StaticComponent.java
+++ b/commands-core/src/main/java/com/intellectualsites/commands/components/StaticComponent.java
@@ -37,18 +37,39 @@ import java.util.Locale;
 import java.util.Queue;
 import java.util.Set;
 
+/**
+ * {@link CommandComponent} type that recognizes fixed strings. This type does not parse variables.
+ *
+ * @param <C> Command sender type
+ */
 public final class StaticComponent<C extends CommandSender> extends CommandComponent<C, String> {
 
     private StaticComponent(final boolean required, @Nonnull final String name, @Nonnull final String... aliases) {
         super(required, name, new StaticComponentParser<>(name, aliases));
     }
 
+    /**
+     * Create a new static component instance for a required command component
+     *
+     * @param name    Component name
+     * @param aliases Component aliases
+     * @param <C>     Command sender type
+     * @return Constructed component
+     */
     @Nonnull
     public static <C extends CommandSender> StaticComponent<C> required(@Nonnull final String name,
                                                                         @Nonnull final String... aliases) {
         return new StaticComponent<>(true, name, aliases);
     }
 
+    /**
+     * Create a new static component instance for an optional command component
+     *
+     * @param name    Component name
+     * @param aliases Component aliases
+     * @param <C>     Command sender type
+     * @return Constructed component
+     */
     @Nonnull
     public static <C extends CommandSender> StaticComponent<C> optional(@Nonnull final String name,
                                                                         @Nonnull final String... aliases) {
@@ -72,7 +93,7 @@ public final class StaticComponent<C extends CommandSender> extends CommandCompo
                                                   @Nonnull final Queue<String> inputQueue) {
             final String string = inputQueue.peek();
             if (string == null) {
-                return ComponentParseResult.failure(this.name);
+                return ComponentParseResult.failure(new NullPointerException("No input provided"));
             }
             for (final String acceptedString : this.acceptedStrings) {
                 if (string.equalsIgnoreCase(acceptedString)) {
@@ -81,7 +102,7 @@ public final class StaticComponent<C extends CommandSender> extends CommandCompo
                     return ComponentParseResult.success(this.name);
                 }
             }
-            return ComponentParseResult.failure(this.name);
+            return ComponentParseResult.failure(new IllegalArgumentException(string));
         }
 
         @Nonnull
diff --git a/commands-core/src/main/java/com/intellectualsites/commands/context/CommandContext.java b/commands-core/src/main/java/com/intellectualsites/commands/context/CommandContext.java
index 4f3e78a3..0b0c71e9 100644
--- a/commands-core/src/main/java/com/intellectualsites/commands/context/CommandContext.java
+++ b/commands-core/src/main/java/com/intellectualsites/commands/context/CommandContext.java
@@ -30,11 +30,21 @@ import java.util.HashMap;
 import java.util.Map;
 import java.util.Optional;
 
+/**
+ * Command context used to assist in the parsing of commands
+ *
+ * @param <C> Command sender type
+ */
 public class CommandContext<C extends CommandSender> {
 
     private final Map<String, Object> internalStorage = new HashMap<>();
     private final C commandSender;
 
+    /**
+     * Create a new command context instance
+     *
+     * @param commandSender Sender of the command
+     */
     public CommandContext(@Nonnull final C commandSender) {
         this.commandSender = commandSender;
     }
diff --git a/commands-core/src/main/java/com/intellectualsites/commands/exceptions/InvalidSyntaxException.java b/commands-core/src/main/java/com/intellectualsites/commands/exceptions/InvalidSyntaxException.java
index 3b575004..ef462f06 100644
--- a/commands-core/src/main/java/com/intellectualsites/commands/exceptions/InvalidSyntaxException.java
+++ b/commands-core/src/main/java/com/intellectualsites/commands/exceptions/InvalidSyntaxException.java
@@ -29,6 +29,9 @@ import com.intellectualsites.commands.sender.CommandSender;
 import javax.annotation.Nonnull;
 import java.util.List;
 
+/**
+ * Exception sent when a {@link CommandSender} inputs invalid command syntax
+ */
 public class InvalidSyntaxException extends CommandParseException {
 
     private final String correctSyntax;
@@ -40,6 +43,11 @@ public class InvalidSyntaxException extends CommandParseException {
         this.correctSyntax = correctSyntax;
     }
 
+    /**
+     * Get the correct syntax of the command
+     *
+     * @return Correct command syntax
+     */
     @Nonnull
     public String getCorrectSyntax() {
         return this.correctSyntax;
diff --git a/commands-core/src/main/java/com/intellectualsites/commands/execution/CommandExecutionCoordinator.java b/commands-core/src/main/java/com/intellectualsites/commands/execution/CommandExecutionCoordinator.java
index 2d102c8b..e8173f21 100644
--- a/commands-core/src/main/java/com/intellectualsites/commands/execution/CommandExecutionCoordinator.java
+++ b/commands-core/src/main/java/com/intellectualsites/commands/execution/CommandExecutionCoordinator.java
@@ -77,7 +77,12 @@ public abstract class CommandExecutionCoordinator<C extends CommandSender> {
     }
 
 
-    public static class SimpleCoordinator<C extends CommandSender> extends CommandExecutionCoordinator<C> {
+    /**
+     * A simple command execution coordinator that executes all commands immediately, on the calling thread
+     *
+     * @param <C> Command sender type
+     */
+    public static final class SimpleCoordinator<C extends CommandSender> extends CommandExecutionCoordinator<C> {
 
         private SimpleCoordinator(@Nonnull final CommandTree<C> commandTree) {
             super(commandTree);
diff --git a/commands-core/src/main/java/com/intellectualsites/commands/execution/CommandExecutionHandler.java b/commands-core/src/main/java/com/intellectualsites/commands/execution/CommandExecutionHandler.java
index 2da19edd..5b2d1560 100644
--- a/commands-core/src/main/java/com/intellectualsites/commands/execution/CommandExecutionHandler.java
+++ b/commands-core/src/main/java/com/intellectualsites/commands/execution/CommandExecutionHandler.java
@@ -45,11 +45,15 @@ public interface CommandExecutionHandler<C extends CommandSender> {
     void execute(@Nonnull final CommandContext<C> commandContext);
 
 
+    /**
+     * Command execution handler that does nothing
+     *
+     * @param <C> Command sender type
+     */
     class NullCommandExecutionHandler<C extends CommandSender> implements CommandExecutionHandler<C> {
 
         @Override
         public void execute(@Nonnull final CommandContext<C> commandContext) {
-
         }
 
     }
diff --git a/commands-core/src/main/java/com/intellectualsites/commands/execution/CommandResult.java b/commands-core/src/main/java/com/intellectualsites/commands/execution/CommandResult.java
index 7a09cd68..8535a31b 100644
--- a/commands-core/src/main/java/com/intellectualsites/commands/execution/CommandResult.java
+++ b/commands-core/src/main/java/com/intellectualsites/commands/execution/CommandResult.java
@@ -23,5 +23,8 @@
 //
 package com.intellectualsites.commands.execution;
 
+/**
+ * The result of a command execution
+ */
 public class CommandResult {
 }
diff --git a/commands-core/src/main/java/com/intellectualsites/commands/parser/ComponentParseResult.java b/commands-core/src/main/java/com/intellectualsites/commands/parser/ComponentParseResult.java
index 637310eb..bb203dc0 100644
--- a/commands-core/src/main/java/com/intellectualsites/commands/parser/ComponentParseResult.java
+++ b/commands-core/src/main/java/com/intellectualsites/commands/parser/ComponentParseResult.java
@@ -26,26 +26,55 @@ package com.intellectualsites.commands.parser;
 import javax.annotation.Nonnull;
 import java.util.Optional;
 
+/**
+ * Result of the parsing done by a {@link ComponentParser}
+ *
+ * @param <T> Parser return type
+ */
 public abstract class ComponentParseResult<T> {
 
     private ComponentParseResult() {
     }
 
+    /**
+     * Indicate that the parsing failed
+     *
+     * @param failure Failure reason
+     * @param <T>     Parser return type
+     * @return Failed parse result
+     */
     @Nonnull
-    public static <T> ComponentParseResult<T> failure(@Nonnull final String failure) {
+    public static <T> ComponentParseResult<T> failure(@Nonnull final Throwable failure) {
         return new ParseFailure<>(failure);
     }
 
+    /**
+     * Indicate that the parsing succeeded
+     *
+     * @param value Value produced by the parser
+     * @param <T>   Parser return type
+     * @return Succeeded parse result
+     */
     @Nonnull
     public static <T> ComponentParseResult<T> success(@Nonnull final T value) {
         return new ParseSuccess<>(value);
     }
 
+    /**
+     * Get the parsed value, if it exists
+     *
+     * @return Optional containing the parsed value
+     */
     @Nonnull
     public abstract Optional<T> getParsedValue();
 
+    /**
+     * Get the failure reason, if it exists
+     *
+     * @return Optional containing the failure reason
+     */
     @Nonnull
-    public abstract Optional<String> getFailure();
+    public abstract Optional<Throwable> getFailure();
 
 
     private static final class ParseSuccess<T> extends ComponentParseResult<T> {
@@ -64,7 +93,7 @@ public abstract class ComponentParseResult<T> {
 
         @Nonnull
         @Override
-        public Optional<String> getFailure() {
+        public Optional<Throwable> getFailure() {
             return Optional.empty();
         }
 
@@ -73,9 +102,9 @@ public abstract class ComponentParseResult<T> {
 
     private static final class ParseFailure<T> extends ComponentParseResult<T> {
 
-        private final String failure;
+        private final Throwable failure;
 
-        private ParseFailure(@Nonnull final String failure) {
+        private ParseFailure(@Nonnull final Throwable failure) {
             this.failure = failure;
         }
 
@@ -87,7 +116,7 @@ public abstract class ComponentParseResult<T> {
 
         @Nonnull
         @Override
-        public Optional<String> getFailure() {
+        public Optional<Throwable> getFailure() {
             return Optional.of(this.failure);
         }
     }
diff --git a/commands-core/src/main/java/com/intellectualsites/commands/parser/ComponentParser.java b/commands-core/src/main/java/com/intellectualsites/commands/parser/ComponentParser.java
index 6d330c90..9523ad1a 100644
--- a/commands-core/src/main/java/com/intellectualsites/commands/parser/ComponentParser.java
+++ b/commands-core/src/main/java/com/intellectualsites/commands/parser/ComponentParser.java
@@ -31,6 +31,12 @@ import java.util.Collections;
 import java.util.List;
 import java.util.Queue;
 
+/**
+ * Parser that parses strings into values of a specific type
+ *
+ * @param <C> Command sender type
+ * @param <T> Value type
+ */
 @FunctionalInterface
 public interface ComponentParser<C extends CommandSender, T> {
 
@@ -44,6 +50,13 @@ public interface ComponentParser<C extends CommandSender, T> {
     @Nonnull
     ComponentParseResult<T> parse(@Nonnull CommandContext<C> commandContext, @Nonnull Queue<String> inputQueue);
 
+    /**
+     * Get a list of suggested arguments that would be correctly parsed by this parser
+     *
+     * @param commandContext Command context
+     * @param input          Input string
+     * @return List of suggestions
+     */
     @Nonnull
     default List<String> suggestions(@Nonnull final CommandContext<C> commandContext, @Nonnull final String input) {
         return Collections.emptyList();
diff --git a/commands-core/src/main/java/com/intellectualsites/commands/sender/CommandSender.java b/commands-core/src/main/java/com/intellectualsites/commands/sender/CommandSender.java
index 65dcefbd..3833b42c 100644
--- a/commands-core/src/main/java/com/intellectualsites/commands/sender/CommandSender.java
+++ b/commands-core/src/main/java/com/intellectualsites/commands/sender/CommandSender.java
@@ -27,8 +27,11 @@ import javax.annotation.Nonnull;
 
 public interface CommandSender {
 
-    default boolean hasPermission(@Nonnull final String permission) {
-        return true;
-    }
+    /**
+     * Check if the command sender has a given permission node
+     *
+     * @param permission Permission node
+     */
+    boolean hasPermission(@Nonnull String permission);
 
 }