Reverse engineer anything with REA: what it does, and the wins that weren't it

In late October, a free tool called REA (short for Reverse Engineer Anything) topped GitHub's weekly trending list and passed 370,000 stars. Around the same time, Replit's CEO Amjad Masad posted that pretty soon all software will be de facto open source. I think he's about half right.

I made a five-minute video on it, and this is the written version with the links and the details I'd want before touching it: what REA does, how AI reverse engineering works under the hood, what people have really done with it, which viral wins never used it, what the sources say about the legal limits, and what it means if your business ships software.

What Reverse Engineer Anything does

REA is a free, open-source add-on that an AI coding agent calls. It works with Claude Code, Codex, Cursor and Gemini CLI. You point it at an app you don't have the source code for and ask how a feature works. It comes back with the answer and the evidence behind it, so you can see what the answer rests on. If you want, you can also get a version of that feature to build into your own project.

The repo isn't new. It came out in April and only started taking off in October, and the technology underneath it is much older than that. What changed is that an AI model now does the slow part.

What you need before you start

• An AI coding agent: Claude Code, Codex, Cursor or Gemini CLI.
• A recent Node.js. In late October the minimums were 22.23.4, 24.22.1 or 26.12.1, depending on which version line you run.
• For many targets, one of the reverse engineering programs REA drives. Ghidra is free, and Hopper and IDA are paid. JavaScript and Electron apps, like Notion, need none of them.
• The official package. Install REA only from github.com/morluto/rea, npm (the package is rea-agents) or rea.tools, because a lookalike repo shipped a trojan in October.
• One setup command. It shows you the changes it will make before it makes them.

How AI reverse engineering works with Claude and REA

The easiest way to picture it is that Claude is the thinker and REA is the toolbox. You ask Claude a question about an app. Claude calls REA, and REA runs established reverse engineering software on your own machine, such as Ghidra, which the US National Security Agency gives away for free, or the paid Hopper and IDA.

Those programs turn an app's machine code back into rough code. That rough code is full of placeholder names that mean nothing to a person, and untangling it by hand is slow work. Claude reads through it, gives each part a proper name and meaning, and explains it back in plain English. That explanation is what you'd use to rebuild a feature in your own app or service.

Desktop apps are only part of it. REA also opens Android apps, websites, games and even AI model files, 33 kinds of target in total.

What people have actually done with REA

This is where the hype and the real use cases split. The three examples below come from REA's own site, its worked examples and its write-up of the Touhou rebuilds, so read them as the project's own reports.

• Aegis, an open-source authenticator app (the kind that gives you a login code). Its code is public, so it's fair game. REA narrowed 3,077 classes down to the path that makes the login codes, and a separate rebuild matched the original on 133 test cases.
• A hacking contest puzzle. REA dug the hidden answer out of a stripped-down program, and the original program accepted it.
• Old Touhou games, rebuilt function by function. On one of them, the source came back for all 1,107 identified functions.

Even the Touhou work has a catch. An audit later found twelve wrong references in functions that had already been signed off. The work looked finished and still had mistakes in it, as AI output often does. I've written about the same pattern at a bigger scale in why a 10-agent fleet only gets you to 60 percent.

What makes those examples believable

Each one had a way to check the answer: 133 test cases for Aegis, a contest program that accepted the answer, and an audit for Touhou. If you use REA yourself, decide how you'll check the result before you trust it. Without a check, a confident explanation is all you've got.

The viral REA wins that weren't REA

A lot of what's been shared online as an REA win didn't use REA at all.

• The parents' TV with the ads stripped off. The post had over 8 million views when I made the video. It credits Claude Code and never mentions REA.
• Modern Warfare 2. A swarm of agents rebuilt 99% of the game's functions using IDA's own MCP (a connector that lets an AI agent drive IDA), not REA. Activision blocked the site hosting it. Here's the write-up.
• WordCraft, an open-source version of Microsoft Word. It was built by watching Word from the outside and reading Word's public file specs, and it's still in alpha.

People are doing the same sort of thing with other devices they own: baby monitors that show ads, picture frames turned into calendars, Lululemon mirrors that had stopped working. 404 Media covered the wider trend in 'Reverse-Engineer Anything' Is the New Wild West of AI. The lesson for judging any of this: if a post doesn't name the tool, don't count it as evidence for that tool.

WordCraft deserves a closer look because of how it was made. Its own rules forbid opening Word's code:

Never read, disassemble or copy anything inside the Word bundle

WordCraft's README

Watching a product from the outside and working from public specs is a different act from opening its code and lifting what's inside. Copying what's inside someone else's software is how people end up in trouble over intellectual property.

The legal limits, as the sources state them

This isn't legal advice, and I'll only repeat what the sources say.

• REA's own rules say it's for software you own, or licensed software you have permission to examine. They don't condone copying licensed material.
• UK law allows decompiling only in a narrow case: making your own program work with the one you decompile, never making something that's basically the same. That's section 50B of the Copyright, Designs and Patents Act 1988. Other countries have their own rules.
• Companies are pushing back. Bethesda, Activision and the makers of Slay the Spire have already gone after projects (Kotaku on the takedowns).
• Studios are getting defensive. One cancelled a public playtest because it was worried about AI clones (Kotaku on ReVamp).

If a plan of yours depends on any of these points, put it to a lawyer before you build anything.

What REA means if you run a software business

1. 1Treat anything you ship as readable. Pricing logic, API connections and keys baked into an app you've shipped can now be read by someone with an AI agent in an afternoon. Keep them out of the app and on a secure server.
2. 2Old systems can be understood again. If a system was built years ago and the person who built it has left, REA can help you work out how it works so you can maintain it, develop it and add features. That holds only if your contract gives you the rights to it.
3. 3A list of features won't protect you. If your product is mostly a list of features, anyone can get the idea in an afternoon and use it. What protects you is your customers and the service around the product.

So, will all software be open source?

Readable, more and more, yes. Free to copy, no. Takedowns have already happened, and I expect plenty more intellectual property claims to follow. That's why I'd only give Masad half: being able to read an app's code doesn't give you the right to copy it, and the lawyers look like the only clear winners.

If you want to look inside your own software, or software you're licensed and permitted to examine, I've written up the safe way to do it, step by step.