I built diff-journal, a small Node.js library for append-only, diff-based journaling of file changes with deterministic replay and rollback.

The core idea is simple:

every file change is recorded as an immutable journal entry (unified diff)

the journal is the single source of truth

files on disk are derived artifacts that can always be rebuilt

This is especially useful for automated or AI-generated file changes, where you want:

strict auditability

deterministic replay (no heuristics, no “best effort” undo)

the ability to materialize any past state by sequence number

It’s intentionally not a VCS and doesn’t try to replace Git.

Repo: https://github.com/svenschaefer/diff-journal

npm: https://www.npmjs.com/package/diff-journal

Feedback very welcome.