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What is the Pokémon Red/Blue Disassembly?

This project is a complete disassembly of the original Pokémon Red and Blue Game Boy games into human-readable assembly language. A disassembly converts compiled machine code back into source code that can be read, understood, modified, and reassembled into working ROMs. The disassembly recreates the exact original games - when built, it produces byte-for-byte identical ROMs to the original releases:
  • Pokémon Red (UE) [S][!].gb - SHA1: ea9bcae617fdf159b045185467ae58b2e4a48b9a
  • Pokémon Blue (UE) [S][!].gb - SHA1: d7037c83e1ae5b39bde3c30787637ba1d4c48ce2
  • BLUEMONS.GB (debug build) - SHA1: 5b1456177671b79b263c614ea0e7cc9ac542e9c4

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Why Does This Matter?

Understanding how these classic games work at the assembly level opens up incredible possibilities:

Learn Game Development

Study the techniques used by Game Freak to create one of the most successful games of all time

Create ROM Hacks

Modify the games to create entirely new Pokémon experiences with custom features

Fix Bugs

Discover and fix original bugs like the Mew glitch or battle mechanics issues

Research & Documentation

Document game mechanics, understand data structures, and preserve gaming history

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Project Structure

The disassembly is organized into logical sections that mirror how the original game was structured: 
pokered/
├── audio.asm          # Sound and music engine
├── main.asm           # Core game logic organized by ROM banks
├── home.asm           # Essential functions in home bank
├── maps.asm           # Map data and scripts
├── text.asm           # All in-game text and dialogue
├── constants/         # Game constants (items, moves, Pokémon, etc.)
├── data/              # Game data (stats, moves, sprites)
├── engine/            # Core game systems (battle, menus, overworld)
├── gfx/               # Graphics data
└── Makefile           # Build configuration
The project uses RGBDS (Rednex Game Boy Development System) to assemble the source files into Game Boy ROMs.

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Key Features

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Complete Documentation

Every function, data table, and constant has been carefully labeled and documented. Instead of cryptic memory addresses, you’ll find readable labels like: 
; From engine/battle/core.asm
CalculateDamage:
    ; Calculate damage for a move
    ld a, [wDamage]
    ld b, a
    ; ... damage calculation logic

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Modular Organization

The code is split into logical modules by functionality:
  • Engine: Battle system, overworld movement, menus, events
  • Data: Pokémon stats, move data, trainer parties, item prices
  • Maps: Town and route layouts, NPC scripts, wild encounters
  • Graphics: Sprites, tilesets, animations

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Build System

A robust Makefile handles building both Red and Blue versions, including:
  • Debug builds with enhanced features
  • Virtual Console patches for 3DS releases
  • Automatic dependency tracking
  • Graphics conversion from PNG to Game Boy format

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What You Can Do

With this disassembly, you can:
1

Study the Code

Understand how classic Game Boy games were developed, including memory management, graphics rendering, and game logic
2

Modify Game Mechanics

Change battle formulas, type effectiveness, experience curves, or add entirely new mechanics
3

Add New Content

Create new Pokémon, moves, items, maps, or trainers
4

Fix Original Bugs

Correct bugs from the original games or balance issues
5

Create Tools

Build tools that generate data for the disassembly or extract information
This project is for educational and research purposes. Creating and distributing ROM hacks may have legal implications depending on your jurisdiction.

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Community and Resources

The Pokémon reverse engineering community (pret) maintains this and many other Pokémon disassembly projects:

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Prerequisites

Before you begin, you should have:
  • Basic understanding of assembly language (or willingness to learn)
  • Familiarity with Git and command-line tools
  • A text editor for editing .asm files
  • Knowledge of how Game Boy games work (helpful but not required)
If you’re new to assembly language, the wiki tutorials provide beginner-friendly guides to get started.

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Next Steps

Ready to get started? Follow these guides in order:

Installation

Set up RGBDS and required tools on your platform

Quick Start

Build your first ROM and verify it works

Build docs developers (and LLMs) love

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