Hacker News — AI on Front Page · October 10, 2026 · 7 min read

REA Reverse – Engineer Anything

Mirrored from Hacker News — AI on Front Page for archival readability. Support the source by reading on the original site.

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Reverse engineering, with your coding agent

Find out how
software works.

REA gives your agent the tools to inspect a program and explain what it does.

See how REA works ↓ Setup guide Showcases →

Already know RE? Skip to analysis guides →

Set up REA

Copy this into your coding agent:

Your coding agent

›Install REA and connect it to this coding agent using npx rea-agents@latest setup. Show me the setup plan for approval, then verify the installation.

Or run this in your terminal:

npx rea-agents@latest setup

Approve the setup plan, then restart your agent.

What is reverse engineering?

Finding out how software works by examining the program itself.

The goal: understand a feature well enough to explain it, change it or rebuild it.

One question: why does Calculator give 220 for 200 + 10%?

Before REA · You investigate it yourself

Original x64 · selected instructions

0x180124945: MOV EAX, dword ptr [R13 + 0x18]
0x180124949: CMP EAX, 0x5c
0x18012494c: JZ 0x180124aba
0x180124952: CMP EAX, 0x5b
0x180124955: JZ 0x180124aba
0x18012495b: MOV EDX, 0x64
0x180124960: LEA RCX, [RSP + 0x160]
0x180124968: CALL 0x180122650
0x18012496e: LEA RDX, [R13 + 0x160]
0x180124975: LEA RCX, [RSP + 0x78]
0x18012497a: CALL 0x180109720
0x18012497f: MOV RSI, RAX
0x180124982: MOV qword ptr [RSP + 0x28], RAX
0x180124987: LEA RDX, [RSP + 0x160]
0x18012498f: MOV RCX, RAX
0x180124992: CALL 0x180123190
; … value-copy instructions omitted …
0x180124a14: MOV RDX, RDI
0x180124a17: LEA RCX, [RSP + 0xf8]
0x180124a1f: CALL 0x180109720
0x180124a24: LEA R8, [RSP + 0x30]
0x180124a29: MOV RDX, RAX
0x180124a2c: LEA RCX, [RSP + 0xb8]
0x180124a34: CALL 0x180123c10

You decode the instructions, follow the calls and reconstruct the calculation.

With REA · You ask your agent

One prompt.

Ask your agent in plain English.

Example prompt · Calculator

›Use REA to inspect Windows Calculator. Why does 200 + 10% give 220?

Example answer · based on the findings

After +, the % button takes a percentage of the first number.

10% of 200 = 20↓200 + 20 = 220

REA supplies The handler’s instructions, decompiled code and calls.

Your agent explains Which branch applies, what it calculates and how to rebuild it.

Selected assembly from the installed Calculator DLL. The thoughts and reply illustrate the findings. Continue with the Calculator example ↓

Let's try two examples. Change a game's speed, then return to Calculator and rebuild its % button.

Example 01 · Chrome’s dinosaur game

Why does the dinosaur get faster?

Goal Rebuild the game with adjustable speed.

Why reverse engineer it? To reproduce its acceleration, we need the rule in the running game: how fast it starts, how much it increases and when it stops.

Play the reconstruction

Speed 6.0 Use the recovered acceleration rule

Original rule: start at 6, then increase toward 13.

Move the slider to set your own speed. Space or Jump clears a cactus.

Enable JavaScript to play the reconstruction. The code and explanation above remain readable.

REA returned

The script actually running in the page. The agent reads its update function and speed settings, then uses that rule in a new game.

Example prompt · Dinosaur game

›Use REA to inspect this dinosaur game. Why does it get faster? Show the speed rule, then build a small version with an adjustable speed.

Inspected target: wayou’s Chromium-derived browser edition.

REA · loaded index.js · selected lines

if (this.currentSpeed < this.config.MAX_SPEED) {
  this.currentSpeed += this.config.ACCELERATION;
}

Start at 6. Add 0.001 each update without a collision, while speed is below 13.

Open the speed lab →

What each part does

01 · REARead the running game’s scriptReturn its actual code and settings to the agent.
02 · Your agentRebuild the rule, add a controlUse the recovered acceleration in a small game with a speed slider.
03 · YouChange the speed and playTry the original acceleration, then choose your own pace.

See the script, checks and how to try the analysis

REA inspected the HTTP browser edition through a local debugging connection and returned the loaded index.js, including its source and digest.

Selected settings from the inspected script

ACCELERATION: 0.001,
MAX_SPEED: 13,
SPEED: 6

We called the original game’s update function in a controlled browser check, with obstacles and automatic scheduling disabled. After 4,000 updates, speed was 10.0; after 10,000, it was 13.0, rounded to one decimal.

The new mini-game keeps that speed rule. Its drawing, jumping and collision code are a small teaching implementation. Open the lab to see the new code and run the same speed check.

To inspect the target yourself, follow the browser connection steps using the dinosaur page. Give your agent that page URL and your local debugging endpoint, then copy the prompt above.

Inspected speed code · Chromium Authors · BSD license

Example 02 · Windows Calculator

Rebuild Calculator’s % button.

We saw why 200 + 10% gives 220. Now let’s recover the rules for both + and ×, and try them.

Goal Build a small calculator that handles both + and × correctly.

Why reverse engineer it? The same button uses different rules after + and ×. We inspect the installed app to find which number the percentage is applied to.

Try the calculation

10% of 200 = 20. Then 200 + 20 = 220.

Interactive illustration of the inspected percentage rule.

REA returned

One branch divides by 100. The other also multiplies by the first number. The agent uses both to recreate the % button.

For this example, previous = 200 and current = 10.

Example prompt · Rebuild the % button

›Use REA to inspect Windows Calculator’s % button. Recover the rules after + and ×, then build a small calculator that uses both.

Readable summary of the % handler

if (operation == multiply || operation == divide) {
  percent = current / 100;
} else {
  percent = current * previous / 100;
}

With + Take 10% of the first number.10% of 200 = 20 → 200 + 20 = 220

With × Turn 10% into 0.1.200 × 0.1 = 20

From the installed app to a working % button

01 · REA reads calc.exeIt launches the Calculator appThe code opens ms-calculator:. The agent then selects the installed app’s library.
02 · REA reads the libraryReturn the % handler’s codeThe function checks the operator and uses the constant 100.
03 · Your agent interprets itExplain and reproduce the rulesCrosscheck the branch with Microsoft’s source, then try + and × above.

See the real code and how the answer was checked

REA · selected original instructions

0x180124945: MOV EAX, dword ptr [R13 + 0x18]
0x180124949: CMP EAX, 0x5c
0x18012494c: JZ 0x180124aba
0x180124952: CMP EAX, 0x5b
0x180124955: JZ 0x180124aba
0x18012495b: MOV EDX, 0x64

Operator IDs · Microsoft’s source

#define IDC_MUL 92      // 0x5c
#define IDC_DIV 91      // 0x5b
#define IDC_PERCENT 118 // 0x76

0x64 = 100

Inspected with REA 4.1.0: Windows Calculator 11.2508.4.0, x64. The readable summary uses names from Microsoft’s public source to explain the recovered branch.

Percentage implementation · Microsoft’s test cases · Native setup guide

Your first investigation

Try REA on a small app.

Download our Notes example, trace its CSV export, and check one changed input.

Try the guided example

Want to go deeper?

Tell your agent what you want to understand or build. With REA, you can work together on anything from cloning this website to reconstructing a game from its executable.

Example prompt · Website

›Use REA to inspect https://rea.tools/. Clone this website for me.

Yes, this one.

Example prompt · Game reconstruction

›Use REA to reconstruct this game from its executable. Recover the gameplay logic in C and test it against the original.

See the DX-Ball case study →

For setup and analysis steps, choose your target:

Native binaries

Inspect functions, strings, references and call relationships in executables and libraries.

Native analysis guide

JavaScript & Electron

Map modules, routes, IPC and native dependencies from an application folder or ASAR archive.

Application workflows

Browser & runtime activity

Capture selected browser or process activity, then compare the results across runs.

Browser observation guide

Any questions?

Read the FAQ, chat with us on Discord, or open a GitHub issue for bugs and feature requests.

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