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Automatic Error Checking


In this chapter, you will learn how to use a tool called LuaCheck to automatically scan your mod for any mistakes. This tool can be used in combination with your editor to provide alerts to any mistakes.

Installing LuaCheck


Simply download luacheck.exe from the Github Releases page.


First, you’ll need to install LuaRocks:

sudo apt install luarocks

You can then install LuaCheck globally:

sudo luarocks install luacheck

Check that it’s installed with the following command:

luacheck -v

Running LuaCheck

The first time you run LuaCheck, it will probably pick up a lot of false errors. This is because it still needs to be configured.

On Windows, open powershell or bash in the root folder of your project and run path\to\luacheck.exe .

On Linux, run luacheck . whilst in the root folder of your project.

Configuring LuaCheck

Create a file called .luacheckrc in the root of your project. This could be the root of your game, modpack, or mod.

Put the following contents in it:

unused_args = false
allow_defined_top = true

globals = {

read_globals = {
    string = {fields = {"split"}},
    table = {fields = {"copy", "getn"}},

    -- Builtin
    "vector", "ItemStack",
    "dump", "DIR_DELIM", "VoxelArea", "Settings",

    -- MTG
    "default", "sfinv", "creative",

Next, you’ll need to test that it works by running LuaCheck. You should get a lot fewer errors this time. Starting at the first error you get, modify the code to remove the issue, or modify the configuration if the code is correct. See the list below.


  • accessing undefined variable foobar - If foobar is meant to be a global, add it to read_globals. Otherwise, add any missing locals to the mod.
  • setting non-standard global variable foobar - If foobar is meant to be a global, add it to globals. Remove from read_globals if present. Otherwise, add any missing locals to the mod.
  • mutating read-only global variable ‘foobar’ - Move foobar from read_globals to globals, or stop writing to foobar.

Using with editor

It is highly recommended that you find and install a plugin for your editor of choice to show you errors without running a command. Most editors will likely have a plugin available.

Checking Commits with Travis

If your project is public and is on Github, you can use TravisCI - a free service to run jobs on commits to check them. This means that every commit you push will be checked against LuaCheck, and a green tick or red cross will be displayed next to them depending on whether LuaCheck finds any mistakes. This is especially helpful for when your project receives a pull request - you’ll be able to see the LuaCheck output without downloading the code.

First, you should visit and sign in with your Github account. Then find your project’s repo in your Travis profile, and enable Travis by flipping the switch.

Next, create a file called .travis.yml with the following content:

language: generic
sudo: false
    - luarocks
  - luarocks install --local luacheck
- $HOME/.luarocks/bin/luacheck .
  email: false

If your project is a game rather than a mod or mod pack, change the line after script: to:

- $HOME/.luarocks/bin/luacheck mods/

Now commit and push to Github. Go to your project’s page on Github, and click ‘commits’. You should see an orange disc next to the commit you just made. After awhile it should change either into a green tick or a red cross depending on the outcome of LuaCheck. In either case, you can click the icon to see the build logs and the output of LuaCheck.