CoreBar

CPU, GPU, RAM and temperature in your menu bar — one status item, four trend charts, every core on the chip.

A hand-written app — 809 lines of Swift plus a 515-line C sensor module — with zero third-party dependencies, no subprocess, and no Python anywhere. It costs ≈13 MiB and 0.26 % of a core where keeping macmon in a Terminal window costs ≈75 MiB.

中文说明 → · Full feature list · Changelog · The talk →

Formerly MacMonBar. Renamed in 0.4.0, after 0.3.0 removed the last thing that ever tied it to another project. Old links to the repository still redirect here.

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Performance at a glance

	Terminal route	CoreBar	Difference
Memory (footprint)	≈ 75 MiB	≈ 13 MiB	−83 %
CPU (2 s refresh)	≈ 0.62 % of a core	0.26 % of a core	−58 %
Incremental power	—	≈ 2.3 mW	≈ 0.07 % of a charge per day
GPU	—	0.000 %	pure AppKit 2D, rasterized on the CPU

Measured, not estimated — ri_phys_footprint via libproc, CPU time over 15-second-plus windows, multiple rounds. Against the last two-process build (v0.2.9, app + macmon pipe child, measured head-to-head in the same session): 21.4 → 12.9 MiB (−40 %) and 0.392 → 0.263 % of a core (−33 %), with readouts bit-identical to macmon. Full methodology, cost decomposition, refresh-interval table, the power calibration and the sample-by-sample parity table: docs/performance.md · docs/macmon.md.

Why CoreBar

• Honest CPU numbers. CPU and per-core utilization are sampled by the app itself through Mach host_processor_info, so all cores appear and the count comes from the kernel. macmon's own cpu_usage_pct is a frequency-weighted residency metric: under a 12-thread all-core load it reports 59.0 % where the true utilization is 99.3 %. How →
• One process, nothing to install. GPU utilization and temperature come from a native C module (src/sensors.c) that talks to libIOReport and AppleSMC/IOHID directly — no child process, no brew install, no JSON parsing. How we dropped the subprocess →
• No Dock icon, no window, nothing to switch to. LSUIElement, so it lives in the menu bar and nowhere else.
• Zero dependencies. AppKit + Foundation + Mach + one C translation unit. No SwiftPM, no Carthage, no vendored code, no Rust, no Python — the toolchain and the runtime are both Python-free.
• Not a widget. Menu bar is the only form that can sample at 2 Hz without keeping a terminal session alive, needs no host app and no App Group — WidgetKit is timeline-driven and throttled to minute granularity, so a widget ends up heavier than the thing it wraps.
• Two disjoint colour systems. Charts use identity hues (blue CPU, rose GPU, cyan memory, purple temperature); the numbers use value hues (green / amber / red by their own thresholds). A chart can never collide with a number wearing the same colour. Design notes →

Install

Requires macOS 13+ on Apple Silicon or Intel (x86_64). Nothing else — there is no companion binary to install.

Download the latest release:

→ Download CoreBar (macOS Universal: Apple Silicon & Intel) → Download CoreBar Intel DMG (Dedicated x86_64)

Unzip, drag CoreBar.app to /Applications, and open it. There is no Dock icon — look at your menu bar.

Or build it from source (needs Xcode Command Line Tools):

git clone https://github.com/HairuoLiu/CoreBar.git
cd CoreBar
./build.sh          # compiles src/main.swift + src/sensors.c → ./CoreBar.app
open CoreBar.app

Start at login

System Settings → General → Login Items & Extensions → Open at Login → + and pick CoreBar.app.

Configure

Click the menu-bar item and pick from the menu: percentage colouring (on), gauges (off), temperature (off), per-core row (on), refresh interval (2 s default; 1 / 2 / 5 s available). Full menu reference: docs/features.md.

For AI agents — installing this unattended

Resolve the machine first: Apple Silicon (arm64) or Intel (x86_64), and macOS 13+ (sw_vers -productVersion). CoreBar is distributed as a Universal Binary supporting both architectures.

#!/usr/bin/env bash
# CoreBar unattended install. Safe to re-run. No Python required.
set -euo pipefail

# 1. CoreBar — resolve the newest release asset instead of hard-coding a version
URL=$(curl -fsSL https://api.github.com/repos/HairuoLiu/CoreBar/releases/latest \
      | grep -o '"browser_download_url": *"[^"]*\.zip"' | head -n 1 \
      | sed 's/.*": *"//; s/"$//')
[ -n "$URL" ] || { echo "没找到 release 资源" >&2; exit 1; }
curl -fsSL "$URL" -o /tmp/CoreBar.zip
rm -rf /tmp/CoreBar-app && mkdir -p /tmp/CoreBar-app
unzip -oq /tmp/CoreBar.zip -d /tmp/CoreBar-app

# 2. install + clear the quarantine bit so it launches without a Gatekeeper prompt
rm -rf /Applications/CoreBar.app
mv /tmp/CoreBar-app/CoreBar.app /Applications/
xattr -dr com.apple.quarantine /Applications/CoreBar.app 2>/dev/null || true

# 3. launch, then confirm the process is alive — it is LSUIElement, so there is no window
open /Applications/CoreBar.app
sleep 2
pgrep -x CoreBar >/dev/null && echo "OK: CoreBar running" || { echo "启动失败" >&2; exit 1; }

Notes for an agent:

• Success is a single process named CoreBar. There is no child process — GPU and temperature are read in-process by the native C sensor module.
• The app does not read anything from disk at launch; no PATH lookups, no install step to verify.
• Do not try to screenshot the app to verify it. It has no window; use pgrep and the menu-bar item's presence.
• To uninstall: quit from the menu, delete /Applications/CoreBar.app. Nothing else is written outside the bundle.

Troubleshooting

Something is wrong — open this

Symptom	Cause	Fix
GPU / temperature show —	The native sensor module could not initialize (rare — a future macOS locking down the private APIs)	Nothing to install. CPU and memory keep working; report the macOS version if it persists.
Everything shows —, including CPU	Should be impossible — CPU has its own timer. Report it.	—
Values sit at 0 % and never move	An old build (≤ 0.1.x) that depended on macmon for all metrics	Update to 0.2.0 or later
Menu bar item gone after a restart	Not registered as a login item	System Settings → General → Login Items & Extensions → Open at Login → +
Menu bar item hidden behind the notch	macOS drops items off the right edge when the bar is full	⌘-drag the item to reorder it, or quit other menu-bar apps
"CoreBar is damaged / cannot be opened"	Gatekeeper quarantine on a downloaded, unsigned build	xattr -dr com.apple.quarantine /Applications/CoreBar.app
xcrun: error: invalid active developer path when building	Command Line Tools not installed	xcode-select --install
swiftc: error: unable to find utility	Same as above	Same as above
Nothing happens after open CoreBar.app	It is LSUIElement — there is no window or Dock icon by design	Look at the menu bar
The panel freezes while the menu is open	Fixed in 0.2.0 (a DispatchQueue.main.async redraw does not run inside NSEventTrackingRunLoopMode)	Update — details
Intel Mac architecture support	Universal Binary (arm64 + x86_64)	Fully supported with physical core aggregation and dual GPU (AMD/Intel) separation
CPU reads differently from Activity Monitor	Expected. Activity Monitor shows frequency-weighted residency, the same metric macmon uses	details

Screenshots

Gauges switched on — the optional level bars:

With the sensors unavailable — CPU and per-core still work, the other two say — instead of 0 %:

Dark mode, temperature enabled, and the degraded panel: docs/screenshots.md.

Learn more

Page	What is in it
TALK.md	The 75-Megabyte Window — an 18-minute talk on the four times measurement caught me being confidently wrong
docs/performance.md	Memory / CPU / power measurements, cost decomposition, refresh-interval table
docs/how-it-works.md	Data flow, the Mach sampler, the C sensor bridge, why macmon's CPU figure differs, the NSMenu event-loop bug
docs/macmon.md	Where the GPU/temperature algorithms come from, why a subprocess was ever used, and how the native C module replaced it
docs/features.md	Every feature, every menu item, every default
docs/design.md	Why the menu bar, why charts, the two colour systems, width as a measured value
docs/tools.md	The measurement scripts, and how the screenshots are generated
CHANGELOG.md	Version history

Credits

• macmon by vladkens — where the GPU and temperature algorithms in src/sensors.c come from. CoreBar re-implements them in C and reads the same private interfaces directly; macmon was used as the reference to verify our numbers bit-for-bit, not as a dependency. MIT.
• Per-core accuracy cross-checked against mactop.

License

MIT — see LICENSE.