Opbox Review 2026: CRDT-Powered Real-Time Text Sync

Syncthing is great at syncing files. Git is great at meaningful checkpoints. But neither handles the messy middle: two machines editing the same text file at the same time. Opbox lives in that gap, using CRDTs to merge concurrent edits without ever producing a conflict copy.

What is Opbox?

Opbox is an experimental daemon that syncs a directory of plain text files between machines in real time. It works at the filesystem level — so you keep your own editor — and merges concurrent edits with CRDTs instead of conflict copies. Syncs run end-to-end encrypted through a shared append-only log on s2.dev, or you self-host with s2-lite.

Key features

• CRDT-based conflict-free merging — behind each file sits a shadow CRDT (via the yrs library, a Rust port of Yjs). Concurrent edits exchange ops through a shared log and merge automatically; all replicas converge on one materialization.
• Local-first, filesystem-level — the files on disk are the source of truth; the daemon only maintains CRDT shadows in the background. Works with Obsidian, Logseq, Vim, VS Code, Helix.
• End-to-end encrypted sync — through s2.dev or your own s2-lite relay; nothing readable ever sits on the relay.
• Editor-agnostic with autosave awareness — tuned for editors configured to autosave, so partial edits flow as CRDT ops in near real time.
• Text-files-only by design — non-UTF-8 bytes are ignored; binaries stay in git or another tool. This keeps sync semantics clean.
• .opboxignore with gitignore seeding — automatically excludes what your .gitignore already excludes, so opbox complements git rather than replacing it.
• Deterministic simulation testing — a turmoil-based harness asserts CRDT invariants (idempotency, commutativity, associativity) and convergence.
• Portable Rust binary — single dependency-light process per machine, including an x86_64-musl Linux target.

Who should use it?

Opbox is for knowledge workers and developers who want true real-time, conflict-free text sync across machines without locking into one app. A writer drafting in iA Writer on a laptop and editing the same files in Vim on a desktop never sees a conflict file. Two developers pair on a repo and run opbox on the source tree (.opboxignore seeds from .gitignore) while keeping meaningful checkpoints in git.

It’s also a natural fit for local AI agent workflows: an agent edits markdown on one machine while you review on another, and the edits merge without conflicts.

How it compares

Syncthing is the general-purpose file sync tool but produces conflict copies on concurrent edits. Obsidian Sync and the LiveSync plugin are CRDT peers but locked inside Obsidian. Opbox generalizes CRDT sync to any directory of text files and any editor. Git remains the checkpoint layer — the two are designed to compose. See more ai-productivity tools for related workflows.

Pros and cons

Pros: CRDT merging eliminates conflict files entirely; editor-agnostic and filesystem-level; local-first; E2E encrypted with a self-hostable relay; strong simulation-testing discipline; MIT-licensed.

Cons: experimental and early (24 stars, 2 forks); text files only; easiest path depends on paid S2.dev; small community; best with autosaving editors; thin docs; no GUI/mobile app.

Pricing

Free (MIT). Self-host s2-lite at $0, or pay for the managed S2.dev log by usage — for a personal markdown vault that’s expected to be cents per month.

FAQ

Does Opbox replace Git? No. It handles the edits between commits; .opboxignore seeds from your .gitignore so the two compose cleanly.

Can I use it with Obsidian? Yes — it’s editor-agnostic and filesystem-level, so Obsidian’s vault syncs in real time across machines without conflict copies.

Is my data encrypted? Yes. CRDT ops sync end-to-end encrypted through s2.dev, or fully self-hosted via s2-lite for complete sovereignty.

Which platforms are supported? Linux and macOS (x86_64-musl portable binary). See more ai-productivity tools for related workflows.