diff --git a/proxy/src/test/java/com/velocitypowered/proxy/command/BrigadierCommandTests.java b/proxy/src/test/java/com/velocitypowered/proxy/command/BrigadierCommandTests.java
index 89c263e1f..7b14acd12 100644
--- a/proxy/src/test/java/com/velocitypowered/proxy/command/BrigadierCommandTests.java
+++ b/proxy/src/test/java/com/velocitypowered/proxy/command/BrigadierCommandTests.java
@@ -2,6 +2,7 @@ package com.velocitypowered.proxy.command;
 
 import static com.mojang.brigadier.arguments.IntegerArgumentType.getInteger;
 import static com.mojang.brigadier.arguments.IntegerArgumentType.integer;
+import static com.mojang.brigadier.arguments.StringArgumentType.word;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.fail;
 
@@ -91,8 +92,7 @@ public class BrigadierCommandTests extends CommandTestSuite {
                       assertEquals(2, context.getNodes().size());
                       callCount.incrementAndGet();
                       return 1;
-                    })
-            )
+                    }))
             .build();
     manager.register(new BrigadierCommand(node));
 
@@ -113,12 +113,73 @@ public class BrigadierCommandTests extends CommandTestSuite {
                     .requires(source -> {
                       callCount.incrementAndGet();
                       return false;
-                    })
-            )
+                    }))
             .build();
     manager.register(new BrigadierCommand(node));
 
     assertHandled("hello world");
     assertEquals(1, callCount.get());
   }
+
+  // Suggestions
+
+  @Test
+  void testArgumentSuggestions() {
+    final var node = LiteralArgumentBuilder
+            .<CommandSource>literal("hello")
+            .then(RequiredArgumentBuilder
+                .<CommandSource, String>argument("argument", word())
+                .suggests((context, builder) -> builder
+                        .suggest("foo")
+                        .suggest("bar")
+                        .suggest("baz")
+                        .buildFuture()))
+            .build();
+    manager.register(new BrigadierCommand(node));
+
+    assertSuggestions("hello ", "bar", "baz", "foo");
+    assertSuggestions("hello ba", "bar", "baz", "foo");
+    assertSuggestions("hello bar", "baz", "foo");
+  }
+
+  // The following 2 tests ensure we strictly follow Brigadier's behavior, even
+  // if it doesn't make much sense.
+
+  @Test
+  void testSuggestsEvenIfImpermissible() {
+    final var node = LiteralArgumentBuilder
+            .<CommandSource>literal("parent")
+            .then(LiteralArgumentBuilder
+                .<CommandSource>literal("child")
+                .requiresWithContext((context, reader) -> fail()))
+            .build();
+    manager.register(new BrigadierCommand(node));
+
+    assertSuggestions("parent ", "child");
+    assertSuggestions("parent chi", "child");
+  }
+
+  @Test
+  void testDoesNotSuggestIfImpermissibleDuringParse() {
+    final var callCount = new AtomicInteger();
+
+    final var node = LiteralArgumentBuilder
+            .<CommandSource>literal("parent")
+            .then(LiteralArgumentBuilder
+                .<CommandSource>literal("child")
+                .requiresWithContext((context, reader) -> {
+                  // CommandDispatcher#parseNodes checks whether the child node can be added
+                  // to the context object. CommandDispatcher#getCompletionSuggestions then
+                  // considers a suggestion context with "parent" as the parent, and considers
+                  // the suggestions of relevant children, which includes "child".
+                  assertEquals(2, context.getNodes().size());
+                  callCount.incrementAndGet();
+                  return false;
+                }))
+            .build();
+    manager.register(new BrigadierCommand(node));
+
+    assertSuggestions("parent child");
+    assertEquals(1, callCount.get());
+  }
 }
diff --git a/proxy/src/test/java/com/velocitypowered/proxy/command/CommandManagerTests.java b/proxy/src/test/java/com/velocitypowered/proxy/command/CommandManagerTests.java
index 40f9349f0..7f63b8401 100644
--- a/proxy/src/test/java/com/velocitypowered/proxy/command/CommandManagerTests.java
+++ b/proxy/src/test/java/com/velocitypowered/proxy/command/CommandManagerTests.java
@@ -157,10 +157,12 @@ public class CommandManagerTests {
     assertTrue(manager.hasCommand("foo"));
   }
 
-  static class DummyCommand implements SimpleCommand {
+  static final class DummyCommand implements SimpleCommand {
 
     static final DummyCommand INSTANCE = new DummyCommand();
 
+    private DummyCommand() {}
+
     @Override
     public void execute(final Invocation invocation) {
       fail();
diff --git a/proxy/src/test/java/com/velocitypowered/proxy/command/RawCommandTests.java b/proxy/src/test/java/com/velocitypowered/proxy/command/RawCommandTests.java
index 5e37be8b9..ca8f3634b 100644
--- a/proxy/src/test/java/com/velocitypowered/proxy/command/RawCommandTests.java
+++ b/proxy/src/test/java/com/velocitypowered/proxy/command/RawCommandTests.java
@@ -3,7 +3,10 @@ package com.velocitypowered.proxy.command;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.fail;
 
+import com.google.common.collect.ImmutableList;
 import com.velocitypowered.api.command.RawCommand;
+import java.util.Collections;
+import java.util.List;
 import java.util.concurrent.atomic.AtomicInteger;
 import org.junit.jupiter.api.Test;
 
@@ -90,4 +93,103 @@ public class RawCommandTests extends CommandTestSuite {
     assertHandled("color red");
     assertEquals(1, callCount.get());
   }
+
+  // Suggestions
+
+  @Test
+  void testSuggestsArgumentsAfterAlias() {
+    final var meta = manager.metaBuilder("hello").build();
+    manager.register(meta, new RawCommand() {
+      @Override
+      public void execute(final Invocation invocation) {
+        fail();
+      }
+
+      @Override
+      public List<String> suggest(final Invocation invocation) {
+        assertEquals("hello", invocation.alias());
+        assertEquals("", invocation.arguments());
+        return ImmutableList.of("world", "people"); // ensures we don't mutate the user's list
+      }
+    });
+
+    assertSuggestions("hello ", "people", "world"); // in alphabetical order
+  }
+
+  @Test
+  void testSuggestsArgumentsAfterPartialArguments() {
+    final var meta = manager.metaBuilder("numbers").build();
+    manager.register(meta, new RawCommand() {
+      @Override
+      public void execute(final Invocation invocation) {
+        fail();
+      }
+
+      @Override
+      public List<String> suggest(final Invocation invocation) {
+        assertEquals("12345678", invocation.arguments());
+        return Collections.singletonList("9");
+      }
+    });
+
+    assertSuggestions("numbers 12345678", "9");
+  }
+
+  @Test
+  void testDoesNotSuggestFirstArgumentIfImpermissibleAlias() {
+    final var callCount = new AtomicInteger();
+
+    final var meta = manager.metaBuilder("hello").build();
+    manager.register(meta, new RawCommand() {
+      @Override
+      public void execute(final Invocation invocation) {
+        fail();
+      }
+
+      @Override
+      public boolean hasPermission(final Invocation invocation) {
+        assertEquals("hello", invocation.alias());
+        assertEquals("", invocation.arguments());
+        callCount.incrementAndGet();
+        return false;
+      }
+
+      @Override
+      public List<String> suggest(final Invocation invocation) {
+        return fail();
+      }
+    });
+
+    assertSuggestions("hello ");
+    assertEquals(1, callCount.get());
+  }
+
+  @Test
+  void testDoesNotSuggestArgumentsAfterPartialImpermissibleArguments() {
+    final var callCount = new AtomicInteger();
+
+    final var meta = manager.metaBuilder("foo").build();
+    manager.register(meta, new RawCommand() {
+      @Override
+      public void execute(final Invocation invocation) {
+        fail();
+      }
+
+      @Override
+      public boolean hasPermission(final Invocation invocation) {
+        assertEquals("foo", invocation.alias());
+        assertEquals("bar baz ", invocation.arguments());
+        callCount.incrementAndGet();
+        return false;
+      }
+
+      @Override
+      public List<String> suggest(final Invocation invocation) {
+        return fail();
+      }
+    });
+
+    assertSuggestions("foo bar baz ");
+    assertEquals(1, callCount.get());
+  }
 }
diff --git a/proxy/src/test/java/com/velocitypowered/proxy/command/SimpleCommandTests.java b/proxy/src/test/java/com/velocitypowered/proxy/command/SimpleCommandTests.java
index f52c8cf3d..3cead1f69 100644
--- a/proxy/src/test/java/com/velocitypowered/proxy/command/SimpleCommandTests.java
+++ b/proxy/src/test/java/com/velocitypowered/proxy/command/SimpleCommandTests.java
@@ -4,7 +4,10 @@ import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.fail;
 
+import com.google.common.collect.ImmutableList;
 import com.velocitypowered.api.command.SimpleCommand;
+import java.util.Collections;
+import java.util.List;
 import java.util.concurrent.atomic.AtomicInteger;
 import org.junit.jupiter.api.Test;
 
@@ -91,4 +94,103 @@ public class SimpleCommandTests extends CommandTestSuite {
     assertHandled("color red");
     assertEquals(1, callCount.get());
   }
+
+  // Suggestions
+
+  @Test
+  void testSuggestsArgumentsAfterAlias() {
+    final var meta = manager.metaBuilder("hello").build();
+    manager.register(meta, new SimpleCommand() {
+      @Override
+      public void execute(final Invocation invocation) {
+        fail();
+      }
+
+      @Override
+      public List<String> suggest(final Invocation invocation) {
+        assertEquals("hello", invocation.alias());
+        assertArrayEquals(new String[0], invocation.arguments());
+        return ImmutableList.of("world", "people"); // ensures we don't mutate the user's list
+      }
+    });
+
+    assertSuggestions("hello ", "people", "world"); // in alphabetical order
+  }
+
+  @Test
+  void testSuggestsArgumentsAfterPartialArguments() {
+    final var meta = manager.metaBuilder("numbers").build();
+    manager.register(meta, new SimpleCommand() {
+      @Override
+      public void execute(final Invocation invocation) {
+        fail();
+      }
+
+      @Override
+      public List<String> suggest(final Invocation invocation) {
+        assertArrayEquals(new String[] { "12345678" }, invocation.arguments());
+        return Collections.singletonList("9");
+      }
+    });
+
+    assertSuggestions("numbers 12345678", "9");
+  }
+
+  @Test
+  void testDoesNotSuggestFirstArgumentIfImpermissibleAlias() {
+    final var callCount = new AtomicInteger();
+
+    final var meta = manager.metaBuilder("hello").build();
+    manager.register(meta, new SimpleCommand() {
+      @Override
+      public void execute(final Invocation invocation) {
+        fail();
+      }
+
+      @Override
+      public boolean hasPermission(final Invocation invocation) {
+        assertEquals("hello", invocation.alias());
+        assertArrayEquals(new String[0], invocation.arguments());
+        callCount.incrementAndGet();
+        return false;
+      }
+
+      @Override
+      public List<String> suggest(final Invocation invocation) {
+        return fail();
+      }
+    });
+
+    assertSuggestions("hello ");
+    assertEquals(1, callCount.get());
+  }
+
+  @Test
+  void testDoesNotSuggestArgumentsAfterPartialImpermissibleArguments() {
+    final var callCount = new AtomicInteger();
+
+    final var meta = manager.metaBuilder("foo").build();
+    manager.register(meta, new SimpleCommand() {
+      @Override
+      public void execute(final Invocation invocation) {
+        fail();
+      }
+
+      @Override
+      public boolean hasPermission(final Invocation invocation) {
+        assertEquals("foo", invocation.alias());
+        assertArrayEquals(new String[] { "bar", "baz", "" }, invocation.arguments());
+        callCount.incrementAndGet();
+        return false;
+      }
+
+      @Override
+      public List<String> suggest(final Invocation invocation) {
+        return fail();
+      }
+    });
+
+    assertSuggestions("foo bar baz ");
+    assertEquals(1, callCount.get());
+  }
 }
diff --git a/proxy/src/test/java/com/velocitypowered/proxy/command/SuggestionsProviderTests.java b/proxy/src/test/java/com/velocitypowered/proxy/command/SuggestionsProviderTests.java
index bc4b9e10d..ff486830a 100644
--- a/proxy/src/test/java/com/velocitypowered/proxy/command/SuggestionsProviderTests.java
+++ b/proxy/src/test/java/com/velocitypowered/proxy/command/SuggestionsProviderTests.java
@@ -17,6 +17,127 @@
 
 package com.velocitypowered.proxy.command;
 
-public class SuggestionsProviderTests {
-  // TODO
+import static com.mojang.brigadier.arguments.StringArgumentType.word;
+import static org.junit.jupiter.api.Assertions.fail;
+
+import com.google.common.collect.ImmutableList;
+import com.mojang.brigadier.builder.LiteralArgumentBuilder;
+import com.mojang.brigadier.builder.RequiredArgumentBuilder;
+import com.velocitypowered.api.command.Command;
+import com.velocitypowered.api.command.CommandSource;
+import com.velocitypowered.api.command.RawCommand;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests {@link Command} implementation-independent suggestion methods of
+ * {@link SuggestionsProvider}.
+ */
+public class SuggestionsProviderTests extends CommandTestSuite {
+
+  @Test
+  void testSuggestsAliasForEmptyInput() {
+    final var meta = manager.createMetaBuilder("foo")
+            .aliases("bar", "baz")
+            .build();
+    manager.register(meta, NoSuggestionsCommand.INSTANCE);
+
+    assertSuggestions("", "bar", "baz", "foo");
+  }
+
+  @Test
+  void testDoesNotSuggestForLeadingWhitespace() {
+    final var meta = manager.createMetaBuilder("hello").build();
+    manager.register(meta, NoSuggestionsCommand.INSTANCE);
+
+    assertSuggestions(" ");
+  }
+
+  @Test
+  void testSuggestsAliasesForPartialAlias() {
+    final var meta = manager.createMetaBuilder("foo")
+            .aliases("bar", "baz")
+            .build();
+    manager.register(meta, NoSuggestionsCommand.INSTANCE);
+
+    assertSuggestions("ba", "bar", "baz");
+    assertSuggestions("fo", "foo");
+    assertSuggestions("bar");
+  }
+
+  @Test
+  void testSuggestsHintLiteral() {
+    final var hint = LiteralArgumentBuilder
+            .<CommandSource>literal("hint")
+            .build();
+    final var meta = manager.createMetaBuilder("hello")
+            .hint(hint)
+            .build();
+    manager.register(meta, NoSuggestionsCommand.INSTANCE);
+
+    assertSuggestions("hello ", "hint");
+    assertSuggestions("hello hin", "hint");
+    assertSuggestions("hello hint");
+  }
+
+  @Test
+  void testSuggestsHintCustomSuggestions() {
+    final var hint = RequiredArgumentBuilder
+            .<CommandSource, String>argument("hint", word())
+            .suggests((context, builder) -> builder
+                    .suggest("one")
+                    .suggest("two")
+                    .suggest("three")
+                    .buildFuture())
+            .build();
+    final var meta = manager.createMetaBuilder("hello")
+            .hint(hint)
+            .build();
+    manager.register(meta, NoSuggestionsCommand.INSTANCE);
+
+    assertSuggestions("hello ", "one", "three", "two");
+    assertSuggestions("hello two", "one", "three");
+  }
+
+  @Test
+  void testSuggestsMergesArgumentsSuggestionsWithHintSuggestions() {
+    final var hint = LiteralArgumentBuilder
+            .<CommandSource>literal("bar")
+            .build();
+    final var meta = manager.createMetaBuilder("foo")
+            .hint(hint)
+            .build();
+    manager.register(meta, new RawCommand() {
+      @Override
+      public void execute(final Invocation invocation) {
+        fail();
+      }
+
+      @Override
+      public List<String> suggest(final Invocation invocation) {
+        return ImmutableList.of("baz", "qux");
+      }
+    });
+
+    // TODO Fix merging
+    assertSuggestions("hello ", "bar", "baz", "qux");
+    assertSuggestions("hello bar", "baz", "qux");
+  }
+
+  static final class NoSuggestionsCommand implements RawCommand {
+
+    static final NoSuggestionsCommand INSTANCE = new NoSuggestionsCommand();
+
+    private NoSuggestionsCommand() {}
+
+    @Override
+    public void execute(final Invocation invocation) {
+      fail();
+    }
+
+    @Override
+    public List<String> suggest(final Invocation invocation) {
+      return ImmutableList.of();
+    }
+  }
 }