A sync protocol for teams
of humans and agents.
Real-time, conflict-free collaboration across editors, agent runtimes, and the browser. Open source. Self-hostable. Written in Rust.
Three primitives, one protocol.
kutl syncs three things through one protocol. Spaces hold which documents exist and who participates. Documents are CRDT-synced text and binary files. Signals are flags, replies, and decisions: protocol-level primitives that travel the same sync channel as document edits.
Every participant runs the daemon on their own machine. A shared relay coordinates. Any tool that reads and writes files becomes a participant: editors, scripts, and AI agents.
Humans and agents interact through the same protocol. Agents call MCP tools; humans use the CLI or in-document syntax (decision headings, @mentions). The primitives are identical underneath.
One protocol for structure, knowledge, and coordination.
The daemon
Watches your local files and translates every edit into CRDT operations. Any tool that reads and writes files (your editor, an AI agent, a script) becomes a sync participant automatically.
The relay
A lightweight WebSocket server that routes operations between participants. Self-host it on your own infrastructure. The relay does not just forward bytes. It reconciles, tracks subscriptions, manages catch-up, and handles the hard parts of distributed coordination.
The engine
Deterministic merging with no conflicts, no manual resolution, and no data loss, regardless of edit ordering or network conditions.
Signals
kutl signals are protocol-level coordination. Flags, replies, and decisions travel through the same relay as document edits. Agents and humans use the same primitives to ask questions, request reviews, and record outcomes.
CRDTs all the way down.
Most sync systems treat the server as a dumb pipe. kutl's relay is an active participant in the CRDT protocol, which means it can solve problems that forwarding alone cannot:
Targeted catch-up
Late joiners and returning clients receive exactly the operations they missed.
Stale client eviction
Slow or unresponsive subscribers are evicted gracefully so one bad connection cannot block everyone.
Document lifecycle
Registration, renames, and deletes tracked with a persistent registry. UUID-based identity survives file moves across machines.
Convergent by design
The CRDT approach extends beyond document content to the entire space. Subscriptions, lifecycle state, and coordination are all modeled as convergent structures. Given the same operations in any order, every participant arrives at the same state. This is a property of the algorithm’s design, and the outcome is always predictable and reproducible.
Central storage is simpler, but it becomes a hard dependency. kutl avoids that. Every participant carries the full document state; no single server keeps your data locked in. The relay coordinates, reconciles, and routes. Shut it down, and nothing is lost.
Works alongside git.
kutl is designed to coexist with git on coding projects. Put kutl content in a kutl/ subfolder: the daemon watches inside, git tracks outside, and kutl surface bridges content into the git tree when you want it there.
Fast enough that sync is invisible.
kutl's CRDT engine is built on diamond-types. Character-by-character sync means edits appear as they happen, not when you save. The protocol is designed so that the cost of collaboration is never visible to the user.
50,000 mixed edits (70% insert, 30% delete). diamond-types implements the eg-walker algorithm (EuroSys 2025, Best Artifact Award). Benchmarked with kutl-bench.
Install
brew install kutl-io/tap/kutlQuick start
Your teammate already set up the space; ask them for the relay URL and space name (or an invite URL).
# Replace with what your teammate sent you (a name, owner/slug, or invite URL).
kutl join shared-notes --relay ws://relay.example.com:9100/ws
# Sync in the background and confirm.
kutl daemon start
kutl statusSee the full getting-started guide for the relay's auth and lifecycle, joining additional spaces, and the daemon's background-process options.
Don't want to run a relay?
kutlhub is the hosted product built on kutl. It runs the relay and provides a batteries-included UI in any browser. If you'd rather not run the protocol yourself, kutlhub is the managed path.