What is the FUR file format?
A .fur file is a Furnace Module, the native project format of Furnace, a free multi-system chiptune tracker written by tildearrow and first released in 2021. Rather than storing finished audio, a .fur file holds everything needed to rebuild a song: the channel layout, patterns of notes and effects, instrument definitions, wavetables, and embedded PCM or ADPCM samples. Furnace can emulate more than 50 retro sound chips, and each module records which of those chips its song targets.
Under the hood the format is a block-based binary file. It opens with the 16-byte magic string -Furnace module-, a 2-byte format version, and then a series of named blocks for song info, instruments, samples, and pattern data. The whole file may be zlib-compressed, which Furnace detects on its own. Format versions are plain integers that have climbed from 27 in Furnace 0.4.6 to 228 in 0.6.8.1 while keeping older files readable.
Security & safety
RISK: LOWA .fur file is passive song data, not an executable, so opening one cannot run code. The only realistic concern is a malformed or malicious file exploiting a parser bug, so open files from unknown sources with an up-to-date Furnace build.
Format details
in a nutshell- Fur / fur brush texture files - Some 3D and hair-grooming plugins use .fur as an ad-hoc extension for fur or hair descriptor data, unrelated to Furnace audio.
- Generic user-named data - The three-letter string 'fur' is occasionally used as a private extension by in-house tools; such files have no shared format.
Programs that open FUR files
Windows1 app
Furnace
Open-source Download the Windows build, then open the .fur file with File > Open to edit and play the module. 
macOS1 app
Furnace
Open-source Grab the macOS .dmg, drag Furnace to Applications, and open the .fur file from within the app. 
Linux1 app
Furnace
Open-source Install from your distro package (e.g. furnace on Arch) or the AppImage, then run furnace song.fur to open it. 
Android1 app
Furnace
Open-source Install the Android APK from the official releases and open the .fur file to play or edit it. Technical details
deep spec| Encoding | Binary block structure; strings are UTF-8 null-terminated |
| Byte order | Little-endian for all multi-byte integers and floats |
| Container | Flat block list: 16-byte magic, 2-byte format version, reserved fields, then named blocks (INFO, SONG, INS, WAVE, SMPL, PATR, etc.) |
| Compression | Optional whole-file zlib (DEFLATE) compression; uncompressed files also accepted |
| Typical size | A few KB to several MB, depending on embedded PCM samples |
| Structure | After the header, each block (format version >= 100) carries a 4-byte identifier and 4-byte little-endian size, followed by its data. Blocks hold song metadata and channel setup, instruments (40+ synthesis types), wavetables, PCM/ADPCM/BRR samples, and 256-row pattern arrays with note, instrument, volume, and effect columns. Multiple SONG blocks provide subsongs sharing the same assets. |
| Integrity | No built-in checksum; integrity relies on the zlib stream when compressed |
| Platforms | Windows, macOS, Linux, Android, FreeBSD |
| Notes | The magic string is written mixed-case as -Furnace module- per the official specification. Format versions are monotonic integers (e.g. 27 for Furnace 0.4.6, 181 for 0.6, 228 for 0.6.8.1); Furnace maintains backward compatibility across the range using version-conditional fields. |
| Initial Release Full | Furnace 0.1 was first released in 2021 by tildearrow. |
| Released | 2021 |
| Latest version | Format version 228 (Furnace 0.6.8.1) |
| Open standard | Yes · royalty-free |
| Specification | github.com |
FUR conversions
Community Q&A
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