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Essential’s Command API provides a powerful, annotation-based system for creating custom commands with automatic argument parsing. The main selling point of this API is that all command arguments are automatically described by the parameters to your handler functions.

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Key Features

  • Automatic Argument Parsing: Command arguments are defined by function parameters
  • Type Safety: Built-in support for primitives (Int, Boolean, String, etc.)
  • Subcommands: Easy creation of nested command structures
  • Optional Arguments: Support for nullable types in Kotlin and Optional in Java
  • Custom Parsers: Extensible argument parsing system
  • Auto-generated Help: Automatic help subcommand generation
  • Tab Completion: Built-in tab completion support

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Basic Structure

To create a command, extend the Command class: 
object MyCommand : Command("mycommand") {
    @DefaultHandler
    fun handle() {
        // Called when user types /mycommand
    }
}
Then register it: 
MyCommand.register()

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Command Components

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Default Handler

A function annotated with @DefaultHandler is invoked when the command is called with no subcommands: 
@DefaultHandler
fun handle() {
    // Handle /mycommand
}

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Subcommands

Functions annotated with @SubCommand create subcommands: 
@SubCommand("reload")
fun reload() {
    // Handle /mycommand reload
}

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Arguments

Arguments are defined by function parameters: 
@DefaultHandler
fun handle(number: Int, message: String?) {
    // number is required, message is optional
}

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Constructor Parameters

When creating a command, you can configure:
  • name: The command name (required)
  • autoHelpSubcommand: Generate automatic help subcommand (default: true)
  • hideFromAutocomplete: Hide from tab completion (default: false)
object MyCommand : Command(
    name = "mycommand",
    autoHelpSubcommand = true,
    hideFromAutocomplete = false
)

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Command Aliases

You can define global aliases for your command: 
object MyCommand : Command("mycommand") {
    override val commandAliases = setOf(
        Alias("mc"),
        Alias("mycmd", hideFromAutocomplete = true)
    )
}

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Next Steps

Creating Commands

Learn how to create your first command

Arguments

Understand the argument parsing system

Subcommands

Create complex command hierarchies

Registry

Register commands and custom parsers

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