Open Asterune
Errors and debugging

Errors and debugging

Inspect script errors, handle expected failures, and diagnose missing instances.

An unhandled script error reports a message and source line, then stops the current thread. Other scripts and event connections continue running.

Inspect values

Use print for diagnostics and warn for warning output. GetFullName identifies an instance by its hierarchy path.

Luau
print(script:GetFullName())
print(workspace:GetChildren())

Handle an expected failure

pcall returns a success flag followed by return values or an error. Handle the failure explicitly. Do not discard the error without reporting or recovery.

Luau
local ok, result = pcall(function()
  return game:GetService("StorageService"):Open("scores"):Get("player-42")
end)
if not ok then
  warn(result)
end

Use assert to check a precondition and error to raise an error explicitly.

Attempt to index nil

This error occurs when code indexes a value that is nil. A missing child is one possible cause. FindFirstChild returns nil when no matching child exists.

Luau
local door = workspace:FindFirstChild("Door")
if door then
  print(door.Position)
end

Check the following conditions beside the failing lookup:

  • The name and parent match the actual hierarchy.
  • A required replicated child has arrived. Use WaitForChild with a timeout on clients.
  • The instance is available on the current execution side. ServerStorage is not replicated to clients.
  • An optional reference exists. Players.LocalPlayer is nil on the server, and Player.Character can be nil between spawns.

Script does not execute

Check Disabled and the execution container. A Script in StarterGui does not execute. A LocalScript in workspace does not execute. Add a diagnostic at the start of the script to confirm execution.

Handler executes repeatedly

Touched reports part contacts. Multiple limbs and repeated contacts can produce several events for one character. Use a cooldown or guard for actions that must run once.

Each Connect call creates a connection. Reconnecting in loops or other handlers can register duplicate callbacks. Disconnect the previous connection before replacing it.

Instance is not visible

Check Parent, visibility properties, position, and execution side. An unanchored part can fall below FallenPartsDestroyHeight and be removed. Client changes may be visible only to that client.

Related documentation