bl4

Borderlands 4 reverse engineering toolkit — save editor, item serial decoder, NCS parser, items database, drop rate analysis, and memory tools.

Crates

Crate	Description
bl4	Core library (crypto, serial codec, save manipulation, manifest)
bl4-cli	Command-line interface (bl4 binary)
bl4-idb	Items database (SQLite/PostgreSQL, sync/async)
bl4-ncs	Nexus Config Store parser (game binary config format)
bl4-community	Community API server (Axum)
bl4-save-editor	GUI save editor (Tauri)
uextract	UE5 IoStore/pak extractor
bl4-preload	LD_PRELOAD instrumentation library

Installation

From source:

git clone https://github.com/monokrome/bl4.git
cd bl4
cargo build --release -p bl4-cli

Binary location: target/release/bl4

Usage

Configuration

bl4 configure --steam-id 76561197960521364
bl4 configure --show

Steam ID is required for encryption/decryption. Find it in your Steam profile URL.

Save Commands

# Decrypt to YAML
bl4 save 1.sav decrypt -o save.yaml
bl4 save 1.sav decrypt > save.yaml

# Encrypt from YAML
bl4 save 1.sav encrypt save.yaml

# Edit in $EDITOR
bl4 save 1.sav edit

# Query values
bl4 save 1.sav get
bl4 save 1.sav get --level
bl4 save 1.sav get --money
bl4 save 1.sav get --info
bl4 save 1.sav get "state.currencies.cash"

# Set values
bl4 save 1.sav set "state.experience[0].level" 50
bl4 save 1.sav set "state.currencies.cash" 999999

# Fog-of-discovery map manipulation
bl4 save 1.sav --map reveal
bl4 save 1.sav --map clear --zone "Crimson Badlands"

# Validate all items in a save
bl4 save 1.sav --validate-items

Item Serial Commands

# Decode a serial
bl4 serial decode '@Ugr$ZCm/&tH!t{KgK/Shxu>k'
bl4 serial decode '@Ugr$ZCm/&tH!t{KgK/Shxu>k' --verbose
bl4 serial decode '@Ugr$ZCm/&tH!t{KgK/Shxu>k' --rarity

# Validate serial legality
bl4 serial validate '@Ugr$ZCm/&tH!t{KgK/Shxu>k'
bl4 serial validate '@Ugr$ZCm/&tH!t{KgK/Shxu>k' --verbose

# Compare two serials
bl4 serial compare '<serial1>' '<serial2>'

# Modify serial (swap parts from source into base)
bl4 serial modify '<base>' '<source>' <parts>

# Batch decode serials to binary
bl4 serial batch-decode serials.txt output.bin

Items Database

Track, identify, and analyze items across saves:

# Initialize database
bl4 idb init

# Import items from a save file
bl4 idb import-save 1.sav --decode

# Decode all serials and populate metadata
bl4 idb decode-all

# List items with filters
bl4 idb list --weapon-type Pistol --manufacturer Jakobs
bl4 idb list --rarity Legendary --format csv

# Show item details
bl4 idb show '<serial>'

# Set metadata with source attribution
bl4 idb set-value '<serial>' name "Terminus" --source ingame

# Publish/pull items to community server
bl4 idb publish --server https://api.example.com
bl4 idb pull --server https://api.example.com

NCS (Nexus Config Store)

Parse and extract data from the game's binary configuration format:

# Scan a directory for NCS file types
bl4 ncs scan /path/to/decompressed/

# Show contents of an NCS file
bl4 ncs show inv0.bin

# Extract manifests (parts database, category names)
bl4 ncs extract -t manifest /path/to/decompressed/ --json

# Search for patterns across NCS files
bl4 ncs search /path/to/decompressed/ "weapon_ps"

# Decompress NCS from a .pak file
bl4 ncs decompress game.pak -o ./ncs/ --raw

# Decompress a single .ncs file
bl4 ncs decompress Nexus-Data-inv0.ncs -o inv0.bin --raw

Regenerating Manifests from Scratch

The manifest is assembled from three data sources: game memory (part indices, usmap schema), PAK assets (manufacturers, weapon types, gear types, elements, rarities, stats), and NCS files (parts database, category names). Requires the research feature: cargo build -p bl4-cli --features research.

The bl4 manifest command runs the full pipeline in one shot:

# Full regeneration from game Paks + memory dump
bl4 manifest /path/to/game/Paks/ -d game.bin

# With a pre-extracted usmap (skips memory dump step)
bl4 manifest /path/to/game/Paks/ -m game.usmap

# Skip memory entirely (NCS + PAK extraction only)
bl4 manifest /path/to/game/Paks/ --skip-memory

# Resume from existing uextract output
bl4 manifest /path/to/game/Paks/ -d game.bin --skip-extract --extracted /tmp/bl4_extract

# Custom output directory
bl4 manifest /path/to/game/Paks/ -d game.bin -o share/manifest/

Output lands in share/manifest/ by default. Individual steps can also be run separately via bl4 memory, bl4 extract, and bl4 ncs.

Drop Rates

Query drop rates and legendary item sources:

# Find where an item drops
bl4 drops find "Terminus"

# List all drops from a specific source
bl4 drops source "Dryl"

# List all known sources or items
bl4 drops list --sources
bl4 drops list --items

Parts Database

Query the parts manifest:

# Find parts for a weapon type
bl4 parts "Jakobs Pistol"

Memory Tools

Read and analyze live game process memory or dump files:

# Attach to live process
bl4 memory info
bl4 memory objects --class WeaponData
bl4 memory fname 12345

# Work with dump files
bl4 memory --dump game.bin info
bl4 memory --dump game.bin scan "48 8B 05 ?? ?? ?? ??"

# LD_PRELOAD instrumentation
bl4 memory preload run -- wine Borderlands4.exe
bl4 memory preload watch /tmp/bl4_log

UE5 Asset Extraction

# Extract all assets from pak files
uextract /path/to/Paks -o extracted/

# Filter by path pattern
uextract /path/to/Paks -f "ItemSerialPart" -o parts/

# List contents without extracting
uextract list /path/to/Paks

Library Usage

[dependencies]
bl4 = "0.6"

use bl4::{decrypt_sav, encrypt_sav, SaveFile, ItemSerial};
use std::fs;

let encrypted = fs::read("1.sav")?;
let yaml_data = decrypt_sav(&encrypted, "76561197960521364")?;
let mut save = SaveFile::from_yaml(&yaml_data)?;

println!("Character: {:?}", save.get_character_name());
println!("Cash: {:?}", save.get_cash());

save.set_cash(999999)?;
let modified_yaml = save.to_yaml()?;
let encrypted = encrypt_sav(&modified_yaml, "76561197960521364")?;
fs::write("1.sav", encrypted)?;

Serial Decoding

use bl4::ItemSerial;

let item = ItemSerial::decode("@Ugr$ZCm/&tH!t{KgK/Shxu>k")?;

if let Some((mfr, wtype)) = item.weapon_info() {
    println!("{} {}", mfr, wtype);
}

let validation = item.validate();
println!("Legality: {}", validation.legality);

Save File Format

.sav -> decrypt (AES-256-ECB) -> decompress (zlib) -> YAML

Key derivation: Steam ID XOR'd with hardcoded base key.

Development

cargo test
cargo clippy --workspace

Disclaimer

Unofficial tools. Borderlands and related trademarks are property of Gearbox Software and 2K. Not affiliated with or endorsed by Gearbox or 2K.

Use at your own risk.

License

BSD-2-Clause