Luau reference

A searchable cheat sheet of Luau syntax and common patterns. Each card links to the lesson that teaches the idea in full.

Hello, world

The classic first program. Every Luau script can call print.

Basics

print("Hello, Roblox!")

Welcome lesson Scripts

Comments

Comments are notes for you (and future-you) — Luau ignores them.

Basics

-- A single-line comment

--[[
  A multi-line
  comment block
]]

Comments

Statements

Semicolons are optional. One statement per line is the usual style.

Basics

local x = 5
print(x)  -- no semicolon needed

Variables

Local variables

Declare values with local. Locals stay inside the block they live in.

Variables & types

local coins = 100
local name = "Ada"
local isReady = true

Variables

Reassigning variables

Variables hold one value at a time — you can change what they hold.

Variables & types

local score = 0
score = score + 10  -- same variable, new value
print(score)        --> 10

The main types

Numbers, strings, booleans, and nil are the core building blocks.

Variables & types

local a = 5          -- number
local b = "hello"    -- string
local c = true       -- boolean
local d = nil        -- "no value yet"

Types

Check a value's type

type() returns the name of a value's type as a string.

Variables & types

print(type("hi"))   --> string
print(type(5))      --> number
print(type(true))   --> boolean
print(type(nil))    --> nil

Types

Multiple assignment

Assign several variables at once, and use it to swap values.

Variables & types

local x, y = 10, 20
x, y = y, x          -- swaps them
print(x, y)          --> 20  10

String basics

Text in Luau is a string. Double or single quotes both work.

Strings

local greeting = "Hello"
local name = 'World'   -- single quotes work too
print(greeting, name)

Strings

Concatenation

Use .. to join strings together.

Strings

local full = "Hello" .. " " .. "World"
print(full)   --> Hello World

Strings

String interpolation

Backticks let you embed values directly inside a string.

Strings

local coins = 42
print(`You have {coins} coins!`)   --> You have 42 coins!

Strings

Common string helpers

The string library covers the day-to-day text operations.

Strings

print(string.upper("hi"))                --> HI
print(string.sub("banana", 1, 3))      --> ban
print(string.find("hello", "ell"))     --> 2  4
print(string.rep("ab", 3))             --> ababab

Arithmetic

The usual math, plus floor division and remainder.

Operators

print(7 + 3)   --> 10
print(7 - 3)   --> 4
print(7 * 3)   --> 21
print(7 / 3)   --> 2.333...
print(7 // 3)  --> 2   (floor division)
print(7 % 3)   --> 1   (remainder)
print(2 ^ 3)   --> 8   (power)

Comparison

Compare values for equality and ordering. ~= means "not equal".

Operators

print(5 == 5)     --> true
print(5 ~= 6)     --> true
print(5 < 6)      --> true
print(5 >= 5)     --> true
print("a" < "b")  --> true

Boolean logic

and, or, and not combine true/false conditions.

Operators

print(true and false)  --> false
print(true or false)   --> true
print(not true)        --> false

Compound assignment

Shorthand for updating a variable with an operation.

Operators

local x = 10
x += 5   -- x is now 15
x *= 2   -- x is now 30
x %= 4   -- x is now 2

if / elseif / else

Run different code depending on a condition.

Control flow

local health = 20

if health <= 0 then
    print("Game over")
elseif health < 30 then
    print("Low health")
else
    print("Doing fine")
end

Conditionals

while loop

Repeat while a condition stays true.

Control flow

local n = 3
while n > 0 do
    print(n)
    n -= 1
end
-- prints 3, 2, 1

Loops

Numeric for loop

Count up (or down) over a range. A third number sets the step.

Control flow

for i = 1, 5 do
    print(i)          -- 1 2 3 4 5
end

for i = 1, 10, 2 do
    print(i)          -- 1 3 5 7 9
end

For loops

break

Exit a loop early from inside it.

Control flow

local n = 0
while true do
    n += 1
    if n >= 10 then break end
end
print(n)  --> 10

Define & call

Bundle code into a named function, then call it with arguments.

Functions

local function greet(name)
    print("Hello, " .. name)
end

greet("Ada")   --> Hello, Ada

Functions

Return values

A function can hand a value back to whoever called it.

Functions

local function double(x)
    return x * 2
end

local result = double(21)
print(result)  --> 42

Function returns

Multiple returns

Return several values at once and capture them all.

Functions

local function minMax(a, b, c)
    return math.min(a, b, c), math.max(a, b, c)
end

local lo, hi = minMax(3, 9, 5)
print(lo, hi)   --> 3  9

Anonymous functions

Functions are values too — pass them around as callbacks.

Functions

local onJoin = function(player)
    print(player.Name .. " joined!")
end

-- Usually used with events or task.spawn:
playerAdded:Connect(onJoin)

Functions Events

Varargs

... accepts any number of extra arguments.

Functions

local function sum(...)
    local total = 0
    for _, value in ipairs({ ... }) do
        total += value
    end
    return total
end

print(sum(1, 2, 3, 4))   --> 10

Create & index

Tables hold multiple values. Lists start at index 1; dictionaries use keys.

Tables

local fruits = { "apple", "banana", "cherry" }
print(fruits[1])   --> apple  (indexes start at 1)

local player = { name = "Ada", level = 5 }
print(player.name)      --> Ada
print(player["name"])   --> Ada (same thing)

Tables

Iterate a dictionary

pairs() visits every key and value.

Tables

local stats = { coins = 100, xp = 250 }

for key, value in pairs(stats) do
    print(key, value)
end

Tables

Iterate a list

ipairs() walks a list in order, 1 to #list.

Tables

local items = { "sword", "shield", "potion" }

for i, item in ipairs(items) do
    print(i, item)
end

Tables

Table helpers

table.insert and table.remove keep lists tidy.

Tables

local list = { 1, 2, 3 }

table.insert(list, 4)   -- { 1, 2, 3, 4 }
table.remove(list, 1)   -- { 2, 3, 4 }

print(#list)            --> 3

task.wait

Pause the current script for a number of seconds.

Tasks & timing

print("starting")
task.wait(1)          -- wait 1 second
print("later!")

task.wait

task.spawn

Run a function without blocking the code after it.

Tasks & timing

task.spawn(function()
    task.wait(1)
    print("spawned, 1 second later")
end)

print("this prints immediately")

task.wait

warn

Print a message that stands out in the Output window.

Debugging

warn("Careful — this value is unexpected")

Print debugging Output & errors

Common mistakes

The two errors beginners hit most: = instead of == and a missing end.

Debugging

-- Using = instead of == in a condition:
if coins = 5 then end   -- error! use ==

-- Forgetting then / end:
if true then
    print("missing end")
-- error: Expected 'end' (to close 'if' at line 1)

Common errors Output & errors