decayfmt: an open-source file format that corrupts itself every time you open it
alex_verem · x · 2026-09-01
Developer Arav Panwar released decayfmt, an open-source Rust tool that makes files decay on access: encode an image or text file, and every open damages the file on disk before showing it — no undo, no recovery from the file alone.
- Decay speed lives in the filename: photo.idcy1 loses 9.5% of pixel data per open; photo.idcy10 scrambles 63% on the first open. Renaming changes how hard the next open hits.
- Corruption comes from OS randomness, so there's no replayable seed to rebuild the original.
- Image transparency is never touched (decay appears as color noise, not holes); text only swaps printable characters, so sentences rot into something that still looks like language.
- The author calls it "a social contract enforced by math" — it isn't encryption or secure deletion, and anyone with a backup or hex editor can beat it.
In an era where digital files copy for free and AI can regenerate almost anything, a tool that makes reading cost part of the file is a deliberately backwards design.
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