Harness

Harness is a native macOS terminal application built entirely in Swift by Robert Courson, available as a signed and notarized DMG for Apple silicon Macs running macOS 15 or later. The project is MIT-licensed and open source, with the full codebase — renderer, multiplexer, daemon, and CLI — published on GitHub. Its latest release is v1.7.1 (build 121), published on June 6, 2026.

What It Is

Harness is a terminal emulator in the same category as iTerm2, Ghostty, or Warp, but written as a single self-contained Swift codebase rather than a UI layer wrapped around third-party components. It ships its own VT parser, Metal GPU renderer, session daemon (HarnessDaemon), and command-line interface (harness-cli), with no external Swift package dependencies beyond Sparkle for auto-updates. The core design goal is that the renderer, multiplexer, workspace model, and agent-awareness layer all behave as one system rather than loosely coupled parts.

GPU Rendering and Display Fidelity

Harness renders every pane on its own Metal engine with a CoreText glyph atlas on the GPU. Box-drawing and block characters are drawn procedurally in code so borders tile without seams at any font size. The renderer supports ligatures, inline images (Sixel, Kitty, and iTerm2 protocols), 24-bit color, accurate sRGB output by default, and opt-in converted Display-P3 vivid color. Damage-driven redraws keep selection drags, find highlights, IME composition, and streaming output cheap; covered or minimized windows stop rendering entirely. ProMotion displays run at full rate. The project ships 490 built-in color themes and supports .harnesstheme export and import.

Session Persistence and the Multiplexer

Sessions, tabs, and splits are owned by HarnessDaemon rather than the app process, so quitting and reopening Harness leaves everything exactly where it was — scrollback included, persisted to disk and restored even across daemon restarts. The built-in multiplexer supports split panes (horizontal and vertical), copy mode, paste buffers, and a command prefix (default Ctrl-A) with a live cheatsheet. The attach-window command composites a full split layout — borders, status line, live panes, active cursor — into any plain terminal, including over SSH, with no separate multiplexer server. Multiple clients can attach the same surface simultaneously; HarnessDaemon sizes shared clients to the smallest attached view.

Agent Awareness

Harness reads the process tree to detect coding agents running inside its panes: Claude Code, Codex, Cursor, Grok, Pi, Hermes, OpenClaw, OpenCode, Aider, Gemini, and Goose are all recognized, each with a brand color and a sidebar chip. When an agent stops or posts an approval prompt, Harness fires a desktop banner notification and marks the pane with a sidebar bell. Cmd+Shift+U jumps directly to the pane that is waiting and skips panes where agents are still working. One-line hook installation (harness-cli install-hooks <agent>) adds richer, explicit notifications for agents that support hooks; agents without a hook mechanism still notify through the built-in activity detection path.

The CLI and Remote Daemons

harness-cli talks to HarnessDaemon over a local Unix socket and exposes the full command set: list-workspaces, list-surfaces, new-session, new-tab, new-split, send-keys, capture-pane, kill-pane, resize-pane, zoom-pane, swap-pane, rename-tab, attach-window, notify, color-check, theme-preview, and more. The daemon and CLI also run on Linux, so a remote or headless box can host sessions that are driven from a local harness-cli --host <name> command over an SSH tunnel. Remote hosts are registered with harness-cli remote add and reuse existing SSH trust with no new credentials.

Update: Harness v1.7.1

The latest release is v1.7.1 (build 121), published June 6, 2026 — nine days after the repository was created on May 27, 2026, indicating rapid early iteration. The repository had 262 stars and 19 forks as of the last recorded update. CI runs on every push: a deterministic test suite, live daemon tests over a real Unix socket and PTY, and a release build. Signed background updates are delivered via Sparkle with EdDSA signatures.