decayfmt is a novel file format written in Rust where every read operation permanently corrupts the file on disk. Created by Arav Pandey, the format encodes decay as a first-class property, meaning there is no recovery without a backup. Files are named with an instability parameter x (e.g., photo.idcy3 or note.tdcy7), where higher values cause more corruption per open.

This is not encryption, DRM, or secure deletion—it's a social contract enforced by mathematics. Text degrades into readable-looking nonsense, while images lose color fidelity. Each open corrupts roughly 9.5% (x=1) to 63% (x=10) of eligible bytes using a cryptographically secure random generator seeded from OS entropy.

The corruption preserves file length and structure but erodes content over time. A read-only file is refused, and concurrent opens may result in fewer corruptions due to race conditions. The project is licensed under the MIT License and available via cargo install or pre-built binaries for major platforms.