Openharness

Harness like a boss.

The ultimate harness for coding agents and beyond. Claude Code at work. Codex at home. Hermes in the cloud. One command center. Start with code. Then follow your curiosity and build across disciplines: CAD, circuits, robots, games and music.

Download · How it works · Beyond code · Harnesses · Device

Every agent, side by side

Claude Code, Codex, Cursor, OpenCode, Devin, Amp, Copilot and seven more.

Every machine, side by side

Your laptop, home server and GPU box in one window. Link each one with a password. No SSH keys. No Tailscale. No port forwarding.

Keyboard first

⌘P finds any harness on any machine. ⇧⌘I jumps to the harness waiting on you. ⌘D splits. Every key remaps.

End-to-end encrypted

Code, keys and keystrokes are sealed on your machine. The relay forwards bytes it can't read.

Fast and light

A native app, not Electron. Close it and your agents keep working.

Idle measurements on an M2 Max:

• ⌘N, ⌘O, ⌘T UI: 11–13 ms median, 15–18 ms p95.
• Local terminal echo: 1.1 ms median, 7.2 ms p95, excluding UI rendering.
• Desktop resources: ~0.1% of one CPU core and 304 MiB, including terminal rendering and scrollback; agent CLIs and the daemon are excluded.

Desktop results use a Release fixture with 16 terminals and 1,000 scrollback lines each. See the workflow and resource benchmarks and remote P2P, TURN and relay results for workloads, slow tails, connection failures and raw data.

Built the way developers work

• Real terminals. Every agent runs in its own tmux pane. Scrollback, colors and keys just work.
• Your CLIs, as they are. Harness never wraps an agent. It reads transcripts and uses the vendor's own hooks.
• A worktree per harness. Start an agent on its own branch. Your working copy stays clean.
• Remap every key. One JSONC file, reloaded on save. Chords up to four strokes.
• Local models. Run open-weight models on your own machines with Grid, Ollama, MLX-LM and vLLM.
• Bytes, not pixels. Remote terminals stream text peer to peer. No remote desktop.
• Open source, all of it. App, CLI, daemon, relay and device, in this repo.

How it works

In the workspace, a harness is one running session of an agent such as Codex or Claude Code, with its own conversation and working context. A tab groups harnesses. Use New Harness to start one and New Tab to group work. Harnesses in the same tab can message each other with harness send: Agent Messages, an experiment of your account, off by default and turned on in Settings ▸ Experimental.

The Store offers harnesses with instructions, tools, and optional viewers for specific crafts. Install a harness, then start it in your workspace. See the Naming System for the complete naming rules.

One daemon per machine runs your agents in tmux. It dials out, so no machine opens a port.

flowchart LR
  subgraph laptop["Your laptop"]
    app["Harness app"] -- loopback --> d1["daemon"]
    d1 --> a1["tmux · Claude Code · Codex"]
  end
  subgraph box["Your GPU box"]
    d2["daemon"] --> a2["tmux · OpenCode · Hermes"]
  end
  device["Harness device"] -- USB --> d1
  d1 <-. "direct WebRTC" .-> d2
  d1 <-- "ciphertext" --> relay["Harness relay · no keys"]
  relay <-- "ciphertext" --> d2