Command Suggestions

Minecraft has a powerful command suggestion system that's used in many places, such as the /give command. This system allows you to suggest values for command arguments to the user, which they can then select from - it's a great way to make your commands more user-friendly and ergonomic.

Suggestion Providers

A SuggestionProvider is used to make a list of suggestions that will be sent to the client. A suggestion provider is a functional interface that takes a CommandContext and a SuggestionBuilder and returns some Suggestions. The SuggestionProvider returns a CompletableFuture as the suggestions may not be available immediately.

Using Suggestion Providers

To use a suggestion provider, you need to call the suggests method on the argument builder. This method takes a SuggestionProvider and returns the modified argument builder with the suggestion provider attached.

CommandRegistrationCallback.EVENT.register((dispatcher, registryAccess, environment) -> {
	dispatcher.register(CommandManager.literal("command_with_suggestions").then(
			CommandManager.argument("entity", RegistryEntryReferenceArgumentType.registryEntry(registryAccess, RegistryKeys.ENTITY_TYPE))
					.suggests(SuggestionProviders.SUMMONABLE_ENTITIES)
					.executes(FabricDocsReferenceCommands::executeCommandWithSuggestions)
	));
});

private static int executeCommandWithSuggestions(CommandContext<ServerCommandSource> context) throws CommandSyntaxException {
	var entityType = RegistryEntryReferenceArgumentType.getSummonableEntityType(context, "entity");
	context.getSource().sendFeedback(() -> Text.literal("Called /command_with_suggestions with entity = %s".formatted(entityType.value().getUntranslatedName())), false);
	return 1;
}

Built-in Suggestion Providers

There are a few built-in suggestion providers that you can use:

Suggestion Provider	Description
SuggestionProviders.SUMMONABLE_ENTITIES	Suggests all entities that can be summoned.
SuggestionProviders.AVAILABLE_SOUNDS	Suggests all sounds that can be played.
LootCommand.SUGGESTION_PROVIDER	Suggests all loot tables that are available.
SuggestionProviders.ALL_BIOMES	Suggests all biomes that are available.

Creating a Custom Suggestion Provider

If a built-in provider doesn't satisfy your needs, you can create your own suggestion provider. To do this, you need to create a class that implements the SuggestionProvider interface and override the getSuggestions method.

For this example, we'll make a suggestion provider that suggests all the player usernames on the server.

public class PlayerSuggestionProvider implements SuggestionProvider<ServerCommandSource> {
	@Override
	public CompletableFuture<Suggestions> getSuggestions(CommandContext<ServerCommandSource> context, SuggestionsBuilder builder) throws CommandSyntaxException {
		ServerCommandSource source = context.getSource();

		// Thankfully, the ServerCommandSource has a method to get a list of player names.
		Collection<String> playerNames = source.getPlayerNames();

		// Add all player names to the builder.
		for (String playerName : playerNames) {
			builder.suggest(playerName);
		}

		// Lock the suggestions after we've modified them.
		return builder.buildFuture();
	}
}

To use this suggestion provider, you would simply pass an instance of it into the .suggests method on the argument builder.

CommandRegistrationCallback.EVENT.register((dispatcher, registryAccess, environment) -> {
	dispatcher.register(CommandManager.literal("command_with_custom_suggestions").then(
			CommandManager.argument("player_name", StringArgumentType.string())
					.suggests(new PlayerSuggestionProvider())
					.executes(FabricDocsReferenceCommands::executeCommandWithCustomSuggestions)
	));
});

private static int executeCommandWithCustomSuggestions(CommandContext<ServerCommandSource> context) {
	String name = StringArgumentType.getString(context, "player_name");
	context.getSource().sendFeedback(() -> Text.literal("Called /command_with_custom_suggestions with value = %s".formatted(name)), false);
	return 1;
}

Obviously, suggestion providers can be more complex, since they can also read the command context to provide suggestions based on the command's state - such as the arguments that have already been provided.

This could be in the form of reading the player's inventory and suggesting items, or entities that are nearby the player.