Rebuild guide

This is how every project here works. Each project can choose its own tools, stack and pace, but they all go through the same steps. The rule that matters most is to study the original, write down what it does, and then build a new version from what you wrote down.

1. Set up REA

REA ("Reverse Engineer Anything") is an open-source MCP server. It gives an AI agent such as Claude Code, Codex, Cursor or Gemini CLI tools to inspect software, and every finding comes with its evidence. Analysis runs on your machine.

You need Node.js 22.19+, 24.11+ or 26+ (or Bun, using bunx instead of npx). Then:

# Register REA with your agent(s) and install its workflow instructions
npx rea-agents setup        # or: bunx rea-agents@latest setup

# Optional: install the CLI globally
npm install --global rea-agents
rea --help

Native binaries (DOS/Windows EXEs, native mobile libraries, console executables) need a disassembler that REA can drive: Ghidra (free), Hopper or IDA. JavaScript, Electron, WASM, .NET, Android APKs and websites can be analyzed without one. Some formats need extra tools. See the REA README for the full list.

Only get REA from its official sources: the morluto/rea repository, rea.tools, or the rea-agents npm package.

2. Pick the right starting point

Different games need different tools. Start from whatever the game was built with:

Original	Where to start
Android APK (Java/Kotlin)	inspect_android_package, search_android_classes, inspect_android_method, decode_android_resources
Native EXE / ELF / Mach-O	binary_overview, list_procedures, procedure_pseudo_code, get_call_graph
.NET / Unity (Mono)	inspect_managed_artifact, inspect_managed_members
Flash-era / HTML5 / Electron	analyze_javascript_application, analyze_web_bundle, recover_javascript_sources
Unknown container or data file	inspect_artifact, extract_artifact, list_strings, read_bytes

You can also run a quick check from the terminal without an agent:

npx -y rea-agents@latest analyze-javascript-application /absolute/path/to/app --json

3. Analyze: ask questions, write specs

Work one system at a time. Good prompts to give your agent:

• "Using REA, find the main game loop in this APK. What is the tick rate, and what does each tick update?"
• "Trace what happens when the player places a building. Which checks run, and what state changes?"
• "Work out the layout of assets/l0_0. Give me a table of the header fields and how entries are indexed."
• "List every network call the game makes at startup, and what the game does when each one fails."
• "Record anything you couldn't resolve as an unknown so we can come back to it."

REA can keep a list of what a rebuild needs to cover and check the rebuild against it, with tools such as record_unknown, build_reconstruction_obligation_ledger and evaluate_reconstruction_coverage. Use them to track what's left.

Turn the answers into specs under projects/<slug>/notes/, one Markdown file per system. A spec describes behavior (rules, timings, formats, edge cases) and cites the evidence behind each claim. Do not commit decompiled code. Constants, struct layouts and file-format tables are fine.

4. Rebuild for the web

Write the new version from the specs, in whatever stack fits the game:

• Small 2D games: plain HTML5 Canvas + JavaScript. The project template has a no-build starter in play/.
• Bigger games: a separate repository with its own build (Bun, Vite, Phaser, PixiJS, Rust→WASM, …). Set repo and play in projects.json so the site links to it, or commit the built output to play/.
• Assets: load them in the browser from the player's own copy of the original (File API, never uploaded), or make new ones. Never commit the original assets.

5. Verify

Record the original (screenshots, input/output traces, save files) and compare it to the rebuild. REA's capture and compare tools (capture_browser_scenario, compare_web_captures, compare_web_screenshots, verify_reconstruction) help when both run somewhere it can observe. When the rebuild matches well enough to play, set the project's status to playable.

Project layout

projects/projects.json   # one entry per game: status, facts, help wanted (drives the site)
projects/<slug>/
├── index.html           # the project page (copy from projects/_template/)
├── notes/               # behavior specs written from REA findings
├── evidence/            # optional: exported REA evidence bundles (no copyrighted code or assets)
└── play/                # the browser rebuild, served at /projects/<slug>/play/

Start a project →