LuaJIT Decompiler Online

LuaJIT Bytecode Is Not Lua Bytecode

This trips up almost everyone. LuaJIT is a separate implementation of the Lua language with its own compiler, its own instruction set and its own bytecode container format. A file produced by luajit -b has nothing in common with one produced by luac beyond the language it started as.

The two are trivially distinguishable by their first bytes:

• Standard Lua — 1B 4C 75 61, that is \x1b followed by Lua, then a version byte such as 0x51 for Lua 5.1.
• LuaJIT — 1B 4C 4A, that is \x1b followed by LJ, then a bytecode version byte.

Because both are routinely saved with a .luac extension, an extension-based tool sends LuaJIT files to a decompiler that cannot possibly read them, and you get an unhelpful parse error. This site reads the header instead of the filename, so a LuaJIT file is routed to a LuaJIT decompiler even if it is named .lua.

Why LuaJIT Bytecode Is Harder

LuaJIT's instruction set was designed for a tracing JIT compiler, not for readability. It has considerably more opcodes than standard Lua, many of them specialised fast paths for common patterns — dedicated instructions for numeric for loops, for table access with constant string keys, for comparison-and-branch fused into one operation.

Those fused instructions are good for the JIT and awkward for a decompiler, because one bytecode instruction can correspond to several lines of source, and the mapping is not always unique. Recovering readable source is therefore a reconstruction rather than a straight inversion, and the output is usually correct but not byte-identical to what was written.

LuaJIT 2.1 made this harder again. Its bytecode dropped some of the redundancy 2.0 carried, so 2.1 files — especially ones compiled with -s to strip debug information — can leave gaps that no decompiler currently recovers. Where the debug info survives, variable names and line numbers come back with it.

Where You Will Meet LuaJIT

• OpenResty and Nginx — the entire lua-nginx-module ecosystem runs on LuaJIT, and precompiled bytecode is a common deployment choice.
• Games — Garry's Mod, Don't Starve, Factorio's mod runtime, and many titles built on Corona SDK or Defold ship LuaJIT bytecode rather than source.
• Android and iOS apps — games with a Lua scripting layer usually bundle the bytecode inside assets/. Upload the APK and open it from there.
• Network appliances — a great deal of embedded firmware uses LuaJIT for its configuration and control plane.

Related Tools

If your file turns out to be standard Lua bytecode, the Lua decompiler handles Lua 5.0 through 5.4. If it is Roblox bytecode, that is a third format again — see the Luau decompiler.

Frequently Asked Questions