Pier
See what is running on your Mac — and which agent started it.
A native macOS menu bar app for listening ports, AI agent attribution,
containers, MCP servers, previews, logs, and process controls.
Pier answers the question that gets harder as agentic development gets busier:
what owns this port, container, or background process?
It inventories the work already running on your Mac, traces listening processes
back to AI coding harnesses and cmux
sessions, and puts the useful actions one click away.
What Pier shows
- Listening ports — TCP and UDP listeners, deduplicated and grouped by owner.
- Agent attribution — Claude Code, Codex, Cursor, Kimi, OpenCode, and other
known harnesses, plus cmux workspace and surface names, and the Ghostty or
Terminal tab a server runs in (grouped by the tab's folder).
- Background activity — Docker containers, Apple
container workloads,
booted Xcode simulators, and MCP server processes, including stopped
containers. Each simulator row shows what the whole device costs in CPU and
memory, and can be shut down (one at a time, or all at once).
- System at a glance — RAM used, swap, and free disk space in the footer,
sized to fit the row so they never add height. The menu bar icon turns yellow
or red when macOS reports memory pressure, so you notice before things slow
down.
- Live context — CPU history, command details, start/stop events, inline web
previews, and available logs.
- Direct controls — open, copy, start, stop, kill, shut down, and explicit
prune actions.
Pier is a menu bar app with no Dock icon. Search, scope filters, sorting, section
collapse state, panel size, and preview width persist between launches.
Quick start
Requirements
- macOS 13 or later
- Xcode 26 or later, including the Command Line Tools
- Optional: Docker Desktop, Apple
container, cmux, and Xcode's
simulators
Build from source
git clone https://github.com/shaaaaawn/pier.git
cd pier
make build
open dist/Pier.app
The local build is ad-hoc signed. macOS may ask you to confirm the first launch.
For day-to-day development, use:
make run # rebuild and relaunch Pier
make check # lint and run the test suite
See Getting started for first-run behavior and
Development for the full build, test, fixture, and probe
workflow.
How it works
Pier combines bounded local probes:
lsof listeners ─┐
ps processes ───┼─> attribution ─> ports grouped by harness or cmux session
cmux sessions ──┘
docker / container / ps ─> containers, simulators, and MCP server activity
Mach VM stats / sysctl / statfs ─> RAM, swap, pressure, and disk glance
Every external integration is optional. If Docker, Apple container, or cmux is
missing or unavailable, Pier keeps working and reports that source's state
without taking down the rest of the panel; a closed cmux is simply not shown.
The system readings are cheap kernel calls, not subprocesses. Simulators are
found in the process list Pier already reads, so watching them costs nothing
extra; xcrun simctl runs only when you ask Pier to shut one down.
Read Architecture for the collection pipeline and code
map.
Privacy by design
Pier inspects sensitive local process information, so its boundaries are
deliberate:
- no telemetry, update checks, or background service API calls;
- no shell interpolation — subprocesses receive argument arrays;
- no command lines or environment variables written to Pier's log;
- previews use a non-persistent web view and block top-level navigation off-host;
- UI preferences and Pier's protected rotating log are the only disk writes.
Pier can display full process command lines in the UI and debug probes. Avoid
putting secrets in command-line arguments. Previewed pages can still request
their own remote subresources; see
Privacy and security for the complete contract.
Documentation
Project status
Pier is early-stage software built and tested on macOS. There is not yet a
notarized downloadable release.
Pier bundles no third-party logos: agent, terminal and Docker icons are read
from the apps installed on your Mac, and an agent you don't have an app for
gets a monogram.
Acknowledgements
Pier's status-item resilience and verification practices were informed by
CodexBar. The full-color app icon lives
in assets/; the menu bar glyph is drawn in code
(Sources/Pier/PierGlyph.swift).
License
Pier is released under the MIT License.
