ReFrontier

ReFrontier is a command-line toolset for modding Monster Hunter Frontier Online. It handles the full round-trip workflow: unpacking, decrypting, and decompressing game files for editing, then compressing, encrypting, and repacking them for use in-game.

Features

Originally based on mhvuze/ReFrontier, ReFrontier has been extensively rewritten. Version 2.0 introduced breaking changes—see MIGRATION_2.0.md for upgrade instructions. You can use any release pre-2.0 for a version fully compatible with the original.

Key features:

• Cross-platform: Works on Windows, Linux, and macOS
• Performance: 4x faster single-threaded, with multithreaded unpacking support
• Round-trip editing: Full support for ECD/EXF encryption and FTXT text repacking
• Single command: Compress and encrypt files in one step
• Reliability: Fixed duplicate filename issues
• Security: Removed memory-unsafe code and outdated libraries
• Text tools: Improved CSV parsing and cleaner fulldump output
• Validation: Non-destructive integrity checking of game files (--validate)
• Diff: Structural comparison of two game files through encryption/compression layers (--diff)

Installation

Download the latest release for your operating system. Unzip the archive to find ReFrontier.exe (or ReFrontier on Linux/macOS).

To get the latest features, you can build from source.

Usage

You can drag-and-drop files or folders onto the executable, or use the command line.

Quick Start

1. Copy mhfdat.bin (or any file or folder) from the MHFrontier dat/ folder to the same directory as the executable.

2. Decrypt and decompress the file:

   ./ReFrontier mhfdat.bin --saveMeta

3. Edit the extracted data (see tools and included utilities).

4. Compress and encrypt:

   ./ReFrontier mhfdat.bin --compress hfi --level 80 --encrypt

5. Replace the original mhfdat.bin with the new file.

For detailed command reference, see ReFrontier/README.md or run:

./ReFrontier --help

Common Options

Option	Description
--help	Display CLI help
--saveMeta	Save metadata files (required for repacking/re-encryption)
--cleanUp	Delete intermediate files
--validate	Check file integrity without writing output
--diff <file>	Structural comparison with another file

Decryption

ReFrontier decrypts (ECD → JPK) and decompresses files by default.

To preserve metadata for later re-encryption, use --saveMeta:

./ReFrontier mhfdat.bin --saveMeta --decryptOnly

Decompression

Decompression replaces the original file. Always backup important data first.

Compressed files are identified by their JKR header (first bytes of the file).

./ReFrontier mhfdat.bin  # Decompress if already decrypted

Data Editing

Once files are decrypted and decompressed, you can edit them using:

• FrontierTextTool - Extract and modify game text
• FrontierDataTool - Extract and modify game data structures
• External tools listed in See Also

Compression

Compress files using --compress <type> --level <level>:

Type	Alias	Algorithm	Ratio
rw	0	No compression (raw)	1:1
hfirw	2	Huffman coding only	~60-90%
lz	3	LZ77 sliding window	~30-70%
hfi	4	Huffman + LZ77 (best)	~20-50%

The --level parameter (1-100) controls compression aggressiveness for lz and hfi only (ignored by rw and hfirw). Diminishing returns above ~80.

./ReFrontier mhfdat.bin --compress hfi --level 80

Output is written to the output/ directory.

For technical details on compression algorithms, see docs/ARCHIVE_FORMATS.md.

Encryption

Encrypt a compressed file with --encrypt:

./ReFrontier mhfdat.bin --encrypt

If a .meta file exists (e.g., mhfdat.bin.meta created during decryption), it will be used. Otherwise, the default ECD key index (4) is used automatically. This works for all known MHF files, but may not match other game versions or regions.

You can compress and encrypt in a single command:

./ReFrontier mhfdat.bin --compress hfi --level 80 --encrypt

Both ECD and EXF encryption formats are fully supported for round-trip editing.

Text File Editing (FTXT)

FTXT text files can be extracted and repacked:

# Extract text with metadata
./ReFrontier text.ftxt --saveMeta

# Edit the generated .txt file, then repack
./ReFrontier text.ftxt.txt --pack

Validation

Check the structural integrity of a game file without writing any output:

./ReFrontier mhfdat.bin --validate

Recursively validates encryption, compression, and archive layers (ECD, EXF, JPK, MOMO, MHA, FTXT) with CRC32 verification and bounds checking.

Diff

Compare two game files structurally, peeling through encryption and compression layers:

./ReFrontier original.bin --diff modified.bin

Useful for verifying round-trip correctness (unpack, edit, repack), comparing game versions, or catching regressions. Exit code 0 means identical, 1 means differences found.

Build

Requires .NET 8.0 SDK.

git clone https://github.com/Houmgaor/ReFrontier.git
cd ReFrontier
dotnet build --configuration Release

The executable will be at ./ReFrontier/bin/Release/net8.0/ReFrontier.exe.

See Also

Related tools and projects:

Project	Description
Monster-Hunter-Frontier-Patterns	Binary file format templates
FrontierTextHandler	Python tool for text editing
MHFrontier-Blender-Addon	Import 3D models
Erupe	MHFrontier private server

Credits

• Based on mhvuze/ReFrontier
• With additional features from chakratos/ReFrontier
• Special thanks to enler for their help!

License

Edits in this project are licensed under the MIT License.

See ReFrontier#2 for license information on the original code.