Dintch

Dintch – check the integrity of your files

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Dintch will tag as many files as you want with their SHA256 digests. Once tagged, you can check at any future date whether they have changed. Tags move with each file, so you can move, copy or duplicate a tagged file and continue to check its integrity. Tags are preserved on all HFS+ and APFS volumes and most other file systems, in many backups including Time Machine, Carbon Copy Cloner and ChronoSync, and across iCloud. First release.
Dintch 1.0 (El Capitan, Sierra, High Sierra, Mojave and Catalina)

Known Issues:

The strangeness of Photos libraries, and tagging them with Dintch

Support pages:

Dintch support

Check file integrity with Dintch 1.0
Dintch 1.0b2 should now run on macOS 10.11 to 10.15
Checking file integrity with Dintch (first beta)
No thanks for the memories
Should we take bit rot seriously?
Beyond Time Machine: 5 Archiving