What REA is
REA stands for Reverse Engineer Anything. It's a free, open source (MIT) tool that plugs into Claude Code as an MCP server, which is the connector that lets Claude use outside tools.
You point Claude at an app and ask how one feature works. REA looks inside the app without needing its source code and hands Claude what it found, including where in the app the feature's code lives. Claude explains it back to you with that evidence, and then it can build a version of the feature in your own project.
On October 12, 2026 it had about 146,000 stars on GitHub, and 126,976 of them came that week. That put it at the top of GitHub's weekly trending page.
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Set it up (one command)
- Check you have Node.js 22.19 or newer. Run
node -vin your terminal. If it's older, install the current version from nodejs.org. - Run
npx rea-agents setupin your terminal. - Pick Claude Code from the list (or whichever agent you use), read the changes it proposes and approve them. It backs up your existing settings first.
- Close Claude Code and open it again so it loads REA.
If you want the rea command for everyday use, npm install --global rea-agents adds it.
The prompt
Open Claude Code in the folder of your own project and paste this, with your app and feature swapped in:
Use REA to understand how [feature] works in [app]. Show me the evidence, then build a similar feature for my project.
It is adapted from the example in REA's README. For example: "Use REA to understand how auto-zoom on clicks works in Recordly."
What it can look inside
- JavaScript apps and desktop apps built on Electron (a lot of desktop apps are) work with just Node.js. This is the easiest place to start.
- Websites need Chrome or another Chromium browser.
- Native Mac, Windows and Linux programs need a decompiler like Hopper, Ghidra or IDA. Setup can install Hopper for you if you approve it.
- Android apps, .NET programs and a lot more each have their own guide on rea.tools.
Use it on apps you're allowed to look at
REA's own disclaimer says it's for lawful research, education, interoperability and software you own or are authorized to examine. So stick to:
- your own apps,
- open source apps, within their license (some, like AGPL ones, require you to open source and credit anything you build from their code),
- apps whose terms allow it.
Use it to learn how a feature is built and then write your own version. Don't use it to lift someone's code or get around a paywall or license.
If something goes wrong
- If you get version errors, your Node.js is too old. Update it and run setup again.
- If Claude doesn't see REA, restart Claude Code.
- REA updates often. Run
npx rea-agents@latest setupevery so often to get the fixes.
