Diagnose uses of undeclared variables

by the strict project Copyright (C) 2010-2022 std.strict authors

License workflow status codecov.io

This is a pure Lua library for detecting access to uninitialized variables from Lua 5.1 (including LuaJIT), 5.2, 5.3 and 5.4. The libraries are copyright by their authors (see the AUTHORS file for details), and released under the MIT license (the same license as Lua itself). There is no warranty.

When using this module, all variables (including functions!) must be declared through a regular assignment (even assigning nil will do) in a strict scope before being used anywhere or assigned to inside a nested scope.


The simplest and best way to install strict is with LuaRocks. To install the latest release (recommended):

    luarocks install std.strict

To install current git master (for testing, before submitting a bug report for example):

    luarocks install https://raw.githubusercontent.com/lua-stdlib/strict/master/std.strict-git-1.rockspec

The best way to install without LuaRocks is to copy the std/strict directory into your package search path.


The strict package returns a callable, which when called returns a strict environment table that requires all variables be declared before use. For compatibility with Lua > 5.1, you must assign this environment table to _ENV; if necessary, setfenv will be called automatically for compatibility with Lua 5.1 and LuaJIT.

   -- For example, use of the global environment from this scope.
   local _ENV = require 'std.strict' (_G)

   -- Or, prevent all access to global environment.
   local _ENV = require 'std.strict' {}

   -- Or, control access to limited environment from this scope.
   local _ENV = require 'std.strict' {
      setmetatable = setmetatable,
      type = type,
      table_unpack = table.unpack or unpack,


The latest release is documented with LDoc. Pre-built HTML files are included in the release tarball.

Bug reports and code contributions

This library is written and maintained by its users.

Please make bug reports and suggestions as GitHub Issues. Pull requests are especially appreciated.

But first, please check that your issue has not already been reported by someone else, and that it is not already fixed by master in preparation for the next release (see Installation section above for how to temporarily install master with LuaRocks).

There is no strict coding style, but please bear in mind the following points when proposing changes:

  1. Follow existing code. There are a lot of useful patterns and avoided traps there.

  2. 3-character indentation using SPACES in Lua sources: It makes rogue TABs easier to see, and lines up nicely with 'if' and 'end' keywords.

  3. Simple strings are easiest to type using single-quote delimiters, saving double-quotes for where a string contains apostrophes.

  4. Save horizontal space by only using SPACES where the parser requires them.

  5. Use vertical space to separate out compound statements to help the coverage reports discover untested lines.


Check for use of undeclared variables

Strict Info

⭐ Stars28
🔗 Source Codegithub.com
🕒 Last Updatea year ago
🕒 Created7 years ago
🐞 Open Issues0
➗ Star-Issue RatioInfinity
😎 Authorlua-stdlib