Pier: a desktop GUI for pi

pi is a coding agent that lives in the terminal, and that is where I use it most of the day. The trouble starts when I have four sessions going in four projects. A terminal shows one at a time, and the one I am looking at is rarely the one that just finished or is waiting for a yes.

Pier is a macOS app for that situation. The sidebar lists every project pi has ever run in and the sessions under each. A session that produced output while I was elsewhere gets an unread marker. One waiting for input gets a different marker, and the Dock icon shows a badge. That was the feature I wanted, and everything else grew around it.

It is still pi

Pier reimplements none of pi. Each open session is a real pi process started in RPC mode, and Pier draws what it sends back. Your models, settings, extensions, and slash commands work because it is the same program running. Quit Pier, type pi -c in the terminal, and you are in the same session.

The only state Pier owns is its own preferences, in ~/.pi/gui/settings.json. Everything else stays in pi's configuration.

What is on screen

The transcript streams as pi produces it: markdown, thinking collapsed by default, tool calls with their output arriving live, and edit diffs inline. The composer has pi's slash commands, @ file mentions, pasted images, and up-arrow history.

While a turn is running you can keep typing. Follow-up prompts wait in a queue, and any one of them can be promoted to a steering message that interrupts the current turn. The header shows the model, the thinking level, a context meter, the git branch, and whatever status text your extensions publish.

Beside the transcript sits a read-only diff of the working tree against HEAD that refreshes as files change, and a login shell in the project directory. Extension dialogs render as sheets, notifications as toasts.

Installing it

The app is ad-hoc signed and not notarized, so the first launch needs a trip to System Settings, Privacy & Security, and Open Anyway. Self-updates from a new release skip that prompt, because the already-installed app is trusted. It needs macOS on Apple silicon and pi 0.85 or newer on your PATH.