What is the G3FC file format?
A .g3fc file is an archive in the Generation 3 File Container format, an open archive format published by G3Pix (Lucas Guimarães) in 2025. It packs one or more files into a single container and compresses them with Zstandard, the same fast algorithm behind the .zst format. On top of compression, G3FC adds two features rarely found together in a consumer archive format: optional AES-256-GCM authenticated encryption, and optional Reed-Solomon Forward Error Correction that lets an archive survive bit rot during long-term storage.
The format begins each file with the ASCII signature G3FC and ends with a 40-byte footer whose magic is G3CE. That footer points to a CBOR-encoded index, so a reader can list and search the contents without scanning the whole file, which is faster than the sequential reads a .tar archive needs. Values are stored little-endian, text is UTF-8, and integrity is protected by CRC-32 checksums. The specification is open, with reference tools in Rust, Go, C#, and Python released under the GNU General Public License v2.0.
Security & safety
RISK: LOWG3FC is a data archive, not an executable, so opening one does not run code. As with any archive, treat files from unknown senders with caution and scan extracted contents. Encrypted archives require the correct password; AES-256-GCM also authenticates the data, so tampering is detected on extraction.
Format details
in a nutshell- G3F (Guitar Pro 3 / fax G3) - The similar-looking .g3f extension is unrelated and refers to older fax or music-notation files, not the G3FC archive.
Programs that open G3FC files
Windows3 apps
G3Pix G3FC Archiver
Open-source Download the official G3FC archiver release, open the app, and choose File then Open to browse and extract the archive contents.
g3fc command-line tool
Open-source Install with cargo install g3fc, then run g3fc extract archive.g3fc to unpack, or g3fc list archive.g3fc to view contents.
File Viewer Plus
Paid Open File Viewer Plus and drag the .g3fc file into the window to inspect the archive without a dedicated extractor. 
macOS2 apps
G3Pix G3FC Archiver
Open-source Download the macOS binary from GitHub releases and open the .g3fc file to list or extract its members.
g3fc command-line tool
Open-source Install with cargo install g3fc, then run g3fc extract archive.g3fc from Terminal to unpack the archive. 
Linux2 apps
G3FC (Snap)
Open-source Install with sudo snap install g3fc, then run g3fc extract archive.g3fc to unpack files under your home directory.
g3fc command-line tool
Open-source Install with cargo install g3fc, then use g3fc list and g3fc extract to inspect and unpack archives. Technical details
deep spec| Encoding | Binary container with a fixed 331-byte header, a data region, a CBOR-serialized file index, an optional FEC region, and a 40-byte footer. |
| Byte order | Little Endian for all multi-byte integers |
| Container | Single-file archive holding one or more member files plus a searchable index |
| Compression | Zstandard (Zstd, RFC 8878); per-file or global mode. CLI default level 6. |
| Encryption | Optional AES-256 in GCM mode. Payload layout: 12-byte nonce, 16-byte auth tag, then ciphertext. Keys derived with PBKDF2-HMAC-SHA256, 32-byte key, recommended 100,000 iterations, using separate 64-byte read and write salts stored in the header. |
| Integrity | CRC-32 (IEEE 802.3 polynomial 0xEDB88320) over file data, the header (bytes 0-276), and the footer (first 32 bytes). Reed-Solomon Forward Error Correction is optional (fec_scheme 1), percentage-based with fec_level 0-50, applied to a Data FEC block and a Metadata FEC block. |
| Typical size | Varies; benchmark compressed roughly 13,000 files (2 GB) into about 1 GB. |
| Structure | Header (magic 'G3FC', version, UUID, timestamps in .NET ticks, index offset/length, compression and encryption flags, salts, KDF iterations, FEC settings, header checksum) -> data region -> file index (CBOR then Zstd, optionally encrypted) -> optional FEC region -> 40-byte footer ending in magic 'G3CE'. |
| Platforms | Windows, macOS, Linux |
| Notes | The index is serialized with CBOR (RFC 8949) and lists per-file path, type, UUID, timestamps, permissions (octal), offsets, sizes, compression flag, and CRC-32. Split archives use block_file_index and chunk grouping fields. Text is UTF-8. Timestamps are 100-nanosecond intervals since 0001-01-01 UTC (.NET ticks). Reference implementations exist in Rust, Go, C#/.NET, and Python. |
| Released | 2025 |
| Latest version | Format version 1.0 (tooling v1.1.3, August 2025) |
| Open standard | Yes · royalty-free |
| Specification | github.com |
G3FC conversions
Community Q&A
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