Borderlands 4 Reverse Engineering Guide

Author

monokrome

Published

December 28, 2025

1 Borderlands 4 Reverse Engineering Guide

Zero to Hero

A comprehensive guide to understanding game internals, reverse engineering techniques, and using the bl4 tooling to analyze and modify Borderlands 4.

1.1 Chapters

1.1.1 Part I: Foundations

Chapter Title Description
1 Binary Basics Hexadecimal, endianness, data types, and memory layout
2 Unreal Engine Architecture UObjects, reflection system, pak files, and usmap

1.1.2 Part II: Analysis Techniques

Chapter Title Description
3 Memory Analysis Process memory, dumps, pattern scanning, pointer chains
4 Save File Format Encryption, compression, YAML structure, key derivation
5 Item Serials Base85 encoding, bit manipulation, token parsing

1.1.3 Part III: Practical Application

Chapter Title Description
6 Data Extraction Pak files, asset parsing, manifest generation
7 Using bl4 Tools Complete CLI reference and practical workflows

1.1.4 Appendices

Appendix Title Description
A SDK Class Layouts Memory layouts for UObject, AOakCharacter, AWeapon, etc.
B Weapon Parts Reference Complete catalog of weapon parts by manufacturer
C Loot System Internals Drop pools, rarity weights, luck system
D Game File Structure Full asset tree and file organization

1.1.5 Reference

Title Description
Glossary Terms, definitions, and quick reference tables

1.2 Quick Start

New to reverse engineering? Start with Chapter 1: Binary Basics and work through sequentially.

Want to edit saves? Jump to Chapter 4: Save File Format.

Need to decode an item? See Chapter 5: Item Serials.

Just want the tool reference? Go to Chapter 7: Using bl4 Tools.

1.3 Prerequisites

Before starting, ensure you have:

  • Basic programming knowledge (any language)
  • Command line familiarity
  • Rust toolchain installed (rustup.rs)
  • The bl4 repository cloned and built
git clone https://github.com/monokrome/bl4
cd bl4
cargo build --release

1.4 About This Guide

This guide accompanies the bl4 project—a Borderlands 4 save file editor and item serial decoder. It documents not just how to use the tools, but why they work, giving you the knowledge to explore further on your own.

Each chapter includes:

  • Concept explanations with visual diagrams
  • Practical examples you can try immediately
  • Exercises to test your understanding
  • Tips from real reverse engineering sessions

For the latest version of this guide, visit book.bl4.dev