REA: an open-source MCP for reverse-engineering any app

tekario @tekari0Originally posted 2026.10.14

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this is the most DANGEROUS repo on GitHub right now REA (Reverse Engineer Anything) is an open source MCP that lets your AI agent take apart how any app works, down to the binary i used it to rebuild the core of a $30/month email app in one weekend. here’s the exact playbook ↓↓↓ 1. install REA into your agent with one command: npx rea-agents setup. it plugs into Claude Code, Codex, Cursor and Gemini CLI 2. point it at the app’s public behavior and map every feature you actually use: keyboard shortcuts, split inbox, snooze, send later, search 3. trace what happens on every action: what loads, what’s cached locally, what talks to the server, how fast each screen responds 4. let REA write it all up as evidence: module maps, data flows, confidence levels. it never hands you their source code, and you don’t want it to 5. feed the findings into Claude Opus 5.5 and ask for a clean-room spec: what each feature does, described in your own words, with zero copied code 6. hand the spec to your agent and rebuild from scratch: your UI, your database, your sync engine, your shortcuts 7. add the features they never shipped: AI triage, auto-replies in your voice, a daily brief, whatever you’ve always wanted 8. test every flow against the original’s observable behavior, fix what’s off, and keep iterating until you prefer your version you end up with your own version of a tool you used to rent, with source code you control and no subscription. works for anything you pay for monthly: → a charting terminal with your own indicators and a backtester → a note-taking app that syncs the way you want → a habit tracker, a CRM, an invoicing tool the prompt ↓ “Use REA to map the publicly observable behavior of [app] for these features: [list]. Write a clean-room specification in your own words: what each feature does, inputs, outputs, edge cases. Don’t include or reproduce any of their code or assets. Then plan a from-scratch implementation in [stack].” the rules so you don’t get burned: → rebuild ideas, never copy code, assets or brand → never bypass a paywall, login or license key → read the license. some ban reverse engineering outright → keep it for yourself, or ship it under your own name and design keep this post and show it to your friends so they know. what’s one subscription you’d kill tomorrow if you could rebuild it?

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