Slash Commands

Mods declare command trees against a loader type — never against Brigadier or a version command class. declareCommands runs once, right after onInitialize, and the tree it leaves behind is plain data; the per-version adapter translates it into the game's dispatcher every time the game builds one (server start and every datapack reload). That split is what keeps a mod's commands working across rebuilds of the dispatcher: a mod that registered into the dispatcher itself would lose its commands on the first reload.

declareCommands

Make the @Mod class implement OMLCommandProvider:

@Mod(id = "my_mod", name = "My Mod", version = "1.0.0")
class MyMod : OMLModInitializer, OMLCommandProvider {

    override fun declareCommands(commands: OMLCommandRegistry) {
        commands.register("mycmd") {
            permissionLevel = 2
            executes { source ->
                source.reply("hello from my_mod, executed by ${source.name}")
            }
            argument("count", OMLArgumentType.INTEGER) {
                executes { source -> source.reply("count=${source.getInt("count")}") }
                subcommand("loud") {
                    executes { source -> source.reply("COUNT=${source.getInt("count")}") }
                }
            }
        }
    }
}

register declares the root literal (/mycmd). subcommand adds a literal child, argument a typed one; executes may sit on any node, including one that has children — /mycmd, /mycmd 5 and /mycmd 5 loud above are three separate handlers. Argument values are read inside the handler by the name given to argument, and only when that argument is on the executed path.

Declaration members

Member	Meaning
subcommand(name) { }	a literal child: /root <name> …
argument(name, type) { }	a typed child: /root <name> <value> …
executes { source -> }	runs when this node terminates the command
permissionLevel	minimum level for this node and everything below it

permissionLevel defaults to 0 (everyone). Nodes at 0 get no check attached at all, so an unprotected subcommand under a protected parent stays protected by the parent.

Argument types

OMLArgumentType	Game parser	Value type	Read with
WORD	single unquoted word	String	getString
STRING	quoted or single word	String	getString
GREEDY_STRING	the rest of the line	String	getString
INTEGER	whole number	Int	getInt
FLOAT	number with fraction	Double	getDouble
BOOLEAN	true / false	Boolean	getBoolean

Each type has exactly one getter. The getters are unchecked casts, so reaching for the wrong one throws ClassCastException inside your handler — the command bridge catches it and answers the invoker with a red [my_mod] command failed: … while logging the stack trace. Reading a name that is not part of the executed path is the same story (… is not part of the executed path).

The command source

Handlers receive one OMLCommandSource per invocation:

Member	Meaning
name	the invoker's display name — Server for the console
hasPlayer	true only when a player ran it (console, function, command block: false)
reply(message)	success channel: chat for a player, plain stdout for the console
replyError(message)	failure channel: rendered red for a player
getString/getInt/getDouble/getBoolean	argument values, by declared name
platform	the raw version source object (CommandSourceStack on 26.x)

platform is the usual escape hatch: reach the player, the level or the permission state the game itself uses when the surface above is not enough.

Permission levels

permissionLevel maps onto the game's operator levels, not onto a number OML invents:

Value	Meaning
0	everyone
1	moderators
2	game masters
3	admins
4+	the server owner

When a declaration stops being a declaration

Translation happens at dispatcher-construction time, in two hook points (the client's and the dedicated server's), and every rebuilt dispatcher is registered into exactly once. Two consequences worth knowing:

• Editing a command tree means a restart. declareCommands ran once, at mod init, and the game keeps using what it was given — a datapack reload rebuilds the dispatcher from the same trees.
• A malformed declaration is contained. Brigadier rejects an empty name, an illegal character or a duplicate root literal; the bridge logs registering /<name> from mod [<id>] failed and skips that one command, so the other mods' commands still land. Two mods claiming the same root literal: the one declared first wins and the other loses with that log line — pick namespaced roots (my_mod_cool rather than cool) if you expect collisions.

Not covered yet

No argument suggestions or tab completion beyond the game's own literal completion, no command aliases, no client-side-only commands. The loader itself registers /oml mods (loaded mods with versions, failed inits in red) and /oml version through this same API, as a working reference beyond the sample mod's /techmod_ping.

Still settling

The command DSL is in the provided, still settling tier: during 0.x its shape may change, with the changes recorded in the release notes. ::