Luau Type System

When to Load

Load this skill when working with Luau type annotations, generics, union types, type narrowing, or sealed/unsealed table behavior. Also load when choosing strictness modes (--!strict vs --!nonstrict), designing module type exports, or typing metatable-backed objects.

Quick Reference

Strictness: --!strict (new code), --!nonstrict (transitional), --!nocheck (legacy only). The New Type Solver (GA Nov 2025) is faster/more accurate.

Inference philosophy: Infer first, annotate boundaries (params, returns, exports). Don't annotate every local — noise hides signal.

Sealed vs unsealed tables:

local t = {}          -- unsealed: can add fields
t.x = 1               -- OK