Types

Core types

CommandCallback

The function passed to usems.register_command. Invoked by the engine whenever a player runs your command, once per dispatch.

type CommandCallback = (...args: string) -> ()

Arguments are the console arguments after the command name, in order.

usems.register_command("my_give", function(item, count)
    -- console: my_give cubecar 3
    print(("give %s x%s"):format(item, count))  --> give cubecar x3
end, 0, "Give an item")

FrameHookCallback

The function passed to usems.hook("frame", ...). Called every rendered frame inside Source’s HudUpdate.

type FrameHookCallback = (dt: number) -> ()

dt is frametime in seconds, read live from the engine’s gpGlobals.

usems.hook("frame", function(dt: number)
    -- integrate anything time-based:
    elapsed += dt
end)

TickHookCallback

The function passed to usems.hook("tick", ...). Called once per server tick inside GameFrame — 66/s in single-player, fixed regardless of frame rate.

type TickHookCallback = () -> ()

usems.hook("tick", function()
    -- fixed-rate simulation logic:
    sim_steps += 1
end)

ModManifest

The parsed mod.toml, as consumed by the loader (see Package Format). Scripts never see this table directly — it’s shown here because usems.mod_name mirrors its name field and validation errors reference these field names.

Field	Type	Rules
id	string	1–64 chars [a-z0-9_.-], starts alphanumeric; unique across packages.
name	string	1–128 chars.
version	string	1–128 chars, free-form.
author	string	1–128 chars.
language	string	"luau" today; others parsed but skipped.
entry	string	Normalized relative path, inside the package, .luau for Luau.
enabled	boolean	Optional, default true.

Value rendering

How print renders each Luau type:

Type	Renders as
string	unquoted text
number (integral)	42
number (fractional)	0.66666666666667
boolean	true / false
nil	nil
table	<table>
function / thread	<function>
userdata	<userdata>
vector	<vector>
error values	<error: message>

Planned types

These arrive with the entity/reflection tiers of Phase 7 and will get their own pages as they land:

• Vector, QAngle, Quaternion, VMatrix — Source math types, native where Luau provides them (vector) and bridged where not
• CBaseEntity and the class hierarchy — entity handles with datamap field access
• EHandle<T> — safe entity references across frames
• trace_t, Ray_t — trace results and inputs for util::TraceLine-style functions
• ConVarRef — live reference to any engine cvar (not just USEMS-registered ones)
• GameEvent — event fields, listen/fire