attempt to index nil with 'X'

What the message means

ServerScriptService.CoinPad:9: attempt to index nil with 'leaderstats'

Other forms of the same message:

• attempt to index nil with 'Humanoid'
• attempt to index nil with 'Character'
• attempt to index nil with number

Luau reads a.b.c one step at a time. If a.b is nil, the next step has nothing to read c from, and the script stops with attempt to index nil with 'c'. When the key is a number, as in list[1], the message ends with number instead of a quoted name.

Everything after the failing line in that function stops running. Other scripts keep going, which is why a game can look half broken: the shop opens, but the coins never arrive.

Causes and fixes

Four things cause this error in practice. Each one below has the smallest code that triggers it, then the fix.

• FindFirstChild found nothing
• Players.LocalPlayer in a server Script
• The character has not spawned yet
• A table entry was never set

FindFirstChild found nothing

FindFirstChild returns nil when there is no child with that exact name. A kill brick is the classic case: whatever touches it is assumed to be part of a character, but a dropped tool, a loose part or an accessory has no Humanoid next to it.

local part = script.Parent

part.Touched:Connect(function(hit)
	-- a loose part has no Humanoid, so FindFirstChild returns nil:
	-- attempt to index nil with 'Health'
	hit.Parent:FindFirstChild("Humanoid").Health = 0
end)

Keep the result in a variable, check it, and only then use it. FindFirstAncestorOfClass("Model") also finds the character when the part that touched is inside an accessory or a held tool.

local part = script.Parent :: BasePart

part.Touched:Connect(function(hit: BasePart)
	local model = hit:FindFirstAncestorOfClass("Model")
	local humanoid = model and model:FindFirstChildOfClass("Humanoid")
	if humanoid then
		humanoid.Health = 0
	end
end)

Players.LocalPlayer in a server Script

Players.LocalPlayer is the player running that copy of the game, so it exists only in LocalScripts and the ModuleScripts they require. In a server Script it is always nil, and the next dot fails, often as attempt to index nil with 'leaderstats' or with 'Character'.

local Players = game:GetService("Players")

-- On the server LocalPlayer is nil: attempt to index nil with 'leaderstats'
local coins = Players.LocalPlayer.leaderstats.Coins
coins.Value += 10

On the server, use the player that an event gives you: PlayerAdded, Touched (through GetPlayerFromCharacter) or the first argument of OnServerEvent.

local Players = game:GetService("Players")

local pad = workspace:WaitForChild("CoinPad") :: BasePart

pad.Touched:Connect(function(hit: BasePart)
	local character = hit:FindFirstAncestorOfClass("Model")
	local player = character and Players:GetPlayerFromCharacter(character)
	if not player then
		return
	end
	local leaderstats = player:FindFirstChild("leaderstats")
	local coins = leaderstats and leaderstats:FindFirstChild("Coins")
	if coins and coins:IsA("IntValue") then
		coins.Value += 10
	end
end)

This pad pays on every touch. A real coin pad also needs a cooldown per player; the leaderboard guide shows how leaderstats are made.

The character has not spawned yet

player.Character is nil until the character first spawns, and for a moment while it respawns. A LocalScript in StarterPlayerScripts runs before that, so reading player.Character.Humanoid at the top of the script fails with attempt to index nil with 'Humanoid'.

local Players = game:GetService("Players")

local player = Players.LocalPlayer
-- Character is nil until the first spawn: attempt to index nil with 'Humanoid'
local humanoid = player.Character.Humanoid
humanoid.WalkSpeed = 24

Use the character that exists, or wait for one with player.CharacterAdded:Wait(), and run your code again on every respawn with CharacterAdded.

local Players = game:GetService("Players")

local player = Players.LocalPlayer

local function onCharacter(character: Model)
	local humanoid = character:WaitForChild("Humanoid", 10)
	if humanoid and humanoid:IsA("Humanoid") then
		humanoid.WalkSpeed = 24
	end
end

if player.Character then
	onCharacter(player.Character)
end
player.CharacterAdded:Connect(onCharacter)

A table entry was never set

Reading a key that is not in a table gives nil, with no error. The error comes one step later, when you read something from that nil. Player data is the usual case: a handler runs before the data for that player has loaded, or after it was removed when they left.

local Players = game:GetService("Players")

local sessionData = {}

Players.PlayerAdded:Connect(function(player)
	task.wait(3) -- stands in for a slow data store load
	sessionData[player] = { Gems = 0 }
end)

local function addGems(player, amount)
	-- before the load finishes: attempt to index nil with 'Gems'
	sessionData[player].Gems += amount
end

Players.PlayerAdded:Connect(function(player)
	addGems(player, 5)
end)

Check that the entry exists before you read from it, and decide what should happen when it does not: skip, queue the change, or wait for the load.

local Players = game:GetService("Players")

type Data = { Gems: number }
local sessionData: { [Player]: Data } = {}

local function addGems(player: Player, amount: number): boolean
	local data = sessionData[player]
	if not data then
		warn(`[Gems] no data for {player.Name} yet`)
		return false
	end
	data.Gems += amount
	return true
end

Players.PlayerAdded:Connect(function(player: Player)
	task.wait(3) -- stands in for a slow data store load
	sessionData[player] = { Gems = 0 }
	addGems(player, 5)
end)

Players.PlayerRemoving:Connect(function(player: Player)
	sessionData[player] = nil
end)

How to find the line that causes it

1. Open Output (Window menu, or the Script tab), clear it with Ctrl+K (⌘K on Mac), and press Play.
2. Find the first red line. It starts with the script's place in the Explorer and the line number, such as ServerScriptService.Shop:12:.
3. Click the red line. Studio opens that script with the cursor on the failing line.
4. Read the lines between Stack Begin and Stack End under it: they list the calls that led there, newest first, so you can see which function called the broken one.
5. Still not sure which value is wrong? Add print(typeof(x), x) just above the line, or set a breakpoint on it and read the values in the Watch window.

Questions

Sources and further reading

• Roblox Creator Docs: Players.LocalPlayer. LocalPlayer is nil on the server
• Roblox Creator Docs: Instance:FindFirstChild. returns nil when no child matches
• Roblox Creator Docs: Player.CharacterAdded
• Luau: type checking. how strict mode flags values that may be nil

How the code was checked: every block marked Fixed passes Luau's strict type checker against Roblox's API definitions (luau-lsp, 23 October 2026), and every block marked Breaks compiles and fails only when it runs. The message wording was checked by running the broken code with the Luau command line tool and against the message strings in Roblox Studio itself on 23 October 2026. A type check catches misspelt APIs and wrong types, not game logic, so playtest in Studio before you publish.