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What Is Luau?

Part of the Introduction To Luau section of Coddy's Lua journey. Lesson 1 of 80.

Luau is a programming language created at Roblox that builds on the Lua you already know by adding gradual static types. Think of it as Lua with an extra layer of safety and tooling. It powers millions of Roblox experiences and has been open source since 2021.

The key idea is that Luau is a superset of Lua 5.1. Any valid Lua 5.1 code is also valid Luau code: you can take a script you wrote in the previous sections and run it as Luau, unchanged.

What Luau adds on top is type annotations. An annotation declares what kind of data a variable should hold, a string, a number, a boolean, a table, so mistakes can be caught before your code even runs:

-- Lua (also valid Luau)
local playerName = "Rio"

-- Luau with a type annotation
local playerName: string = "Rio"

The word gradual matters: annotations are optional. You can type one variable, one function, or a whole file: untyped Lua-style code keeps working while you add types at your own pace.

In return you get better editor tooling, more readable code, and protection against the kind of bugs that plain Lua only reveals while the program is running.

challenge icon

Challenge

Easy

Turn this Lua variable into a typed Luau variable.

  1. On the line local message = "Hello World", add : string right after message.
  2. Keep the print(message) line as it is.

Press Run Code: the output shows Hello World.

Try it yourself

-- Plain Lua: message has no type yet
local message = "Hello World"
print(message)

All lessons in Introduction To Luau

1Getting Started with Luau

What Is Luau?Why Use Luau?Your First Luau CodeType Checking & Error ModesRecap: Introduction to Luau

4Working with Functions

Typing Params & Return ValuesTyping Anonymous FunctionsFunctions Returning NothingOptional ParametersDefault Parameter ValuesDefaults for BooleansVariadic FunctionsDefining Function TypesRecap: Typed Functions

7Project: Typed Task Manager

Project: The Task ShapeFunction to Add a TaskProject lessonFunction to Change Task StatusProject lessonFunction: List Tasks by StatusProject lessonFunction: Print Task SummaryProject lessonCommand Loop: AddProject lessonCommand Loop: List and DoneProject lessonCommand Loop: SummaryProject lesson

10Project: Generic Inventory

Project: Inventory ItemFunction: Add ItemsProject lessonThe Weapons ListProject lessonFunction: Find Item By IDProject lessonSpecific Inventory TypesProject lessonFunction: Describe ItemsProject lessonAnswer Item QueriesProject lesson

2Core Types

Number, String and BooleanThe 'any' Type: Escape HatchThe 'unknown' TypeNil & Optional TypesType Inference in ActionExplicit Type AnnotationsRecap: Core Types Practice

5Aliases, Unions, Intersections

Type Aliases for PrimitivesUnion TypesWorking with Union TypesLiteral TypesIntersection TypesCombining Type AliasesRecap: Advanced Type Combos

8Enums, the Luau Way

The Enum Pattern in LuauNumeric Enums with TablesString Enums as UnionsUsing Literal Union EnumsFreezing Constant TablesRecap: Enums, the Luau Way

11Advanced Topics

Type AssertionsType Guards With typeofThe never TypeNil Safety In Strict ModeIndex SignaturesRecap: Config Value TypesRecap: Fine-Tuning Types

3Typed Tables: Arrays & Maps

Typed ArraysAdding and Reading ElementsWhat is a Map Type?Declaring and Accessing MapsIterating TablesMixed-Shape TablesReading a GridBuilding a Gridtable.unpackRecap: Arrays and Maps

6Typing Table Shapes

Inline Shape AnnotationsType Aliases for ShapesOptional PropertiesShapes vs. Loose TablesExtending ShapesAdding Methods to ShapesSelf and Colon MethodsRecap: Defining Table Shapes

9Generics: A First Look

The Problem Generics SolveA Generic Identity FunctionUsing a Generic FunctionGeneric ArraysGeneric Type AliasesRecap: Generic Functions

Practice on your own: Online Luau compiler