A terminal multiplexer with a workspace sidebar. No agent supervision. No configuration homework.

I built Kiwa because I liked Herdr's workspace sidebar more than I liked paying its CPU bill. I wanted a multiplexer, not something watching my terminal output to work out what my AI agent was doing. I'll leave the AI coding controls to tools like Paseo.

Tmux is the performance benchmark, but I didn't want another configuration project just to get a comfortable workspace sidebar. Herdr got that part right. Zellij wasn't my answer either. Its 52.5 MB executable was a lot of multiplexer for someone who mostly wanted a column on the left.

So Kiwa keeps the sidebar and does less.

The name comes from the Japanese 際（きわ）, meaning "edge" or "boundary". A fitting name for the bit of UI I wanted on the left.

• A persistent workspace sidebar, with tabs and split panes for each project.
• Useful defaults. Install it, run kiwa, and start working. No config file required.
• Keyboard navigation and mouse controls. Click to switch, drag to resize, right-click for actions.
• Compact dividers or individual pane frames with space between them. Zoomed tabs show [Z].
• Detach without stopping your programs. Reattach when you need them.
• Layout restore after a server restart, including workspace directories, splits, names, and zoom. Restored panes start new shells, not the old programs.
• Scrollback, keyboard selection, and clipboard copy through OSC 52.
• Directory and foreground-program tab names, Git branch display, and unread-output markers. No agent-status detective work.

Kiwa is written in Zig and uses Ghostty's ghostty-vt terminal engine. It works inside your existing terminal on Linux and Apple silicon macOS. It is not a terminal emulator app or an AI agent manager.

The comparison below is a historical snapshot from October 6, 2026, not a measurement of the latest commit. Kiwa used ReleaseFast product code at dcd6ecd, with benchmark code at 1565702. The other versions were tmux 3.7c, Zellij 0.45.1, and Herdr 0.9.3.

Executable and download sizes on Linux x86_64, in decimal MB:

Tmux has the smaller executable. Kiwa's Linux binary includes its dependencies. Tmux's library total depends on the distribution and does not mean those libraries are unique to tmux. Kiwa and Zellij downloads are gzip archives; Herdr's is a bare executable.

CPU below is the median percentage of one core, summed across server and client. Lower is better.

Herdr's sidebar was the inspiration. Its idle CPU usage was the motivation.

Memory is server RSS at the end of the sample, not peak memory. Client RSS is separate.

These are three-run results on a four-core Intel N97, at 100×40, with a 6-second warmup and 12-second sample. Kiwa keeps its sidebar and tab row; tmux's status line is off. Kiwa's scrolling result uses an outer terminal with left and right margins. Without them, it measured 0.444% CPU. Both overlap tmux's measured range, so scrolling is a tie here, not a claimed win.

The workloads have fixed output rates. They measure multiplexer overhead, not maximum throughput or input latency. Pane programs and the outer terminal emulator are excluded. This is a comparison of the tested configurations, not proof that one program is universally faster.

Full results, ranges, output bytes, caveats, and reproduction commands.

On Linux x86_64 or ARM64, or an Apple silicon Mac running macOS 13 or later:

curl -fsSL https://raw.githubusercontent.com/txchen/kiwa/master/install.sh | sh
kiwa

The installer verifies the release checksum and puts kiwa in ~/.local/bin. Make sure that directory is on your PATH. Set KIWA_INSTALL_DIR for another location or KIWA_VERSION to pin a release.

Kiwa starts its background server if needed, then attaches. Click + new in the sidebar to create a workspace, or use the shortcuts below. New workspaces ask for a directory. New tabs use the workspace directory; splits inherit the focused pane's directory.

The default prefix is Ctrl+b. Release it, then press the next key. Press Ctrl+b twice to send it to the pane.

Mouse selection copies to your clipboard when the outer terminal allows OSC 52 writes. Programs that request mouse input receive it inside their panes.

kiwa              # attach or start
kiwa ls           # list workspaces and tabs
kiwa --version    # print version and pinned Ghostty commit

After upgrading, kiwa kill-server stops the old server and its pane programs. The next kiwa restores the layout with new shells. Detach instead when you want programs to keep running.

Full usage guide covers all shortcuts, workspace directories, mouse behavior, copy mode, session restore, and environment variables.

First startup creates a commented example at ~/.config/kiwa/config.toml, or under $XDG_CONFIG_HOME. Omitted settings keep their built-in defaults.

[keys]
prefix = "ctrl+a"

[ui]
sidebar_width = 30

kiwa config path      # find your config file
kiwa config check     # validate edits
kiwa reload-config    # apply without restarting pane programs

Saving alone does not reload. Invalid configuration leaves live settings unchanged.

Complete configuration reference covers every setting, action, key syntax, and reload rule. kiwa config guide provides the reference for your installed version without network access.

Install mise, then use the Zig version pinned in mise.toml:

mise install
mise exec -- zig build
mise exec -- zig build test
mise exec -- zig build e2e
mise exec -- zig build -Doptimize=ReleaseFast

The binary is zig-out/bin/kiwa. The default target is static x86_64-linux-musl. On an Apple silicon Mac, add -Dtarget=aarch64-macos.13.0 to build and test commands.

End-to-end tests need git, Python 3, less, Vim, htop, fzf, and ncurses utilities and terminfo. They use private sockets and state directories, not your running session. Do not use --watch or -fincremental; Zig 0.16 incremental compilation crashes on this project.

To reproduce the comparison on Linux with Python 3 and tmux installed:

mise exec -- zig build bench -Doptimize=ReleaseFast -- --runs 5

The benchmark downloads pinned Zellij and Herdr releases on its first run. bench-check also checks Kiwa's CPU and memory budgets against tmux.

Kiwa's main design constraint is work only in response to events. An idle pane should not need a babysitter, including one written in Zig.

Development guide covers testing, cross-compilation, CI, and releases. GLOSSARY.md defines the model; architecture decisions explain the implementation choices.