iob-bar

A tiny macOS menubar app that shows your current insulin on board (IOB).

That's it. No graphs, no blood-sugar tracking, no carb logging, no notifications, no charts. Just the number, and a fast way to log a dose so you don't accidentally double-dose.

⚠️ Not a medical device. This is a personal tool built to help one person remember whether they just took insulin. It is not approved by the FDA or any regulatory body, makes no medical claims, and is not a substitute for professional medical advice or your prescribed insulin regimen. The pharmacokinetic curve is a mathematical approximation — real insulin behavior varies by person, by injection site, by meal composition, by activity level, by stress, by ambient temperature, by everything. Treat the IOB number as a memory aid, not as truth. Use at your own risk.

Who this is for

This app is built for MDI (multiple daily injection) users on pens with half-unit dosing — e.g., Humalog Junior KwikPen. That assumption shapes several design choices that might otherwise look like omissions:

• Quick-add buttons are in 0.5u increments (+0.5 / +1.0 / +1.5 / +2.0)
• No carb counting, no bolus-wizard math
• No pump integration (if you're on a pump, Loop or another AID stack is what you actually want)
• No CGM / blood-glucose display (a separate companion app for that is on the roadmap)

If you're on full-unit pens, the math still works but the quick-add buttons won't match your dosing granularity.

What it does

A small text item lives in your menubar showing your current insulin on board:

2.5u

Click it (or hit ⌃⌥⌘I from anywhere on macOS) to drop down a popover:

• The current IOB in big numerals
• Every dose still active in your system, with how much each one is currently contributing after pharmacokinetic decay
• Four big quick-add buttons (+0.5u / +1.0u / +1.5u / +2.0u), with keyboard shortcuts 1–4
• A custom-amount-and-time entry for when you forgot to log earlier
• Optional AM/PM basal tracking (or once-per-day, or off entirely) that resets at midnight
• Hover over any active dose to reveal an × button that removes it from the IOB calculation

Doses older than the action-duration window (default 6 hours) are pruned automatically — the popover only ever shows what's actually still doing something.

How the math works

The decay curve is the modern exponential model used by LoopKit, parameterized by peak activity time and total action duration. Default parameters target Humalog (75-min peak, 6-hour duration); to use another rapid- acting insulin preset, edit Settings.swift (a settings UI is on the roadmap).

Total IOB at any moment is sum(dose_i × fractionRemaining_i(elapsed_i)), where fractionRemaining is the biexponential pharmacokinetic curve. The implementation is in InsulinModel.swift, derived from LoopKit's ExponentialInsulinModel under Apache 2.0; see NOTICE.

Build and run

Requirements

• macOS Sonoma (14.0) or later
• Xcode 15 or later (free from the Mac App Store)
• A free Apple ID for local code signing — no paid Developer account is required for personal use

Steps

git clone https://github.com/gpechenik/iob-bar.git
cd iob-bar
open iob-bar.xcodeproj

In Xcode:

1. Click the project root in the navigator → select the iob-bar target
2. In the Signing & Capabilities tab, set Team to your Apple ID
3. ⌘R to build and run

The first time you press ⌃⌥⌘I while another app is focused, macOS will prompt you to grant Accessibility / Input Monitoring permission so the global hotkey can fire. Grant it via System Settings → Privacy & Security.

Install for daily use

Once you've run the app once via ⌘R, you have a built iob-bar.app bundle on disk that doesn't require Xcode to launch. To make it part of your day-to-day environment:

1. Find the bundle: in Xcode's project navigator, expand the Products group at the bottom → right-click iob-bar.app → Show in Finder. Or navigate to ~/Library/Developer/Xcode/DerivedData/iob-bar-<hash>/Build/Products/Debug/iob-bar.app.
2. Copy to /Applications/: drag the .app into your Applications folder.
3. Auto-launch on login (optional): System Settings → General → Login Items → click the + under "Open at Login" → pick iob-bar from the Applications folder.

For a smaller, optimized Release-configuration build, use Product → Archive → Distribute App → Copy App in Xcode. For personal use the Debug build works fine.

Code signing note: apps signed with a free Apple ID work indefinitely on the Mac that signed them, but other Macs will see them as "unidentified developer" and Gatekeeper will challenge them on first launch. To distribute beyond your own machine cleanly, you need a paid Apple Developer ID (~$99/year).

Storage

Doses, basal stamps, and settings live as plain JSON in:

~/Library/Containers/<bundle-id>/Data/Library/Application Support/iob-bar/

The App Sandbox transparently redirects the canonical Application Support path to a per-app container, so this is where the data actually lives. The <bundle-id> matches whatever you set during project creation (e.g. graham.gg.iob-bar). Nothing leaves your machine.

Cross-machine sync via symlink (optional)

If you want the same dose history across multiple Macs, you can symlink the storage directory to a synced location (iCloud Drive, Dropbox, syncthing, etc.). On the first Mac:

# Quit iob-bar first.
BUNDLE_ID="graham.gg.iob-bar"  # change to yours
SYNC_DIR="$HOME/Library/Mobile Documents/com~apple~CloudDocs/iob-bar"

# Move existing data into the synced location:
mv "$HOME/Library/Containers/$BUNDLE_ID/Data/Library/Application Support/iob-bar" \
   "$SYNC_DIR"

# Replace the original location with a symlink:
ln -s "$SYNC_DIR" \
      "$HOME/Library/Containers/$BUNDLE_ID/Data/Library/Application Support/iob-bar"

On a second Mac, after building and running the app once (so the container exists), only the second step is needed — point a fresh symlink at the same $SYNC_DIR.

macOS occasionally recreates container subdirectories during system updates or when sandbox grants change. If your symlink gets clobbered, recreate it. If that happens often enough to be annoying, that's the natural prompt to migrate to HealthKit-backed storage — see ROADMAP.md.

Keyboard shortcuts

Global

Combo	Action
⌃⌥⌘I	Toggle the popover from anywhere

In the popover

Key	Action
1	Log +0.5u
2	Log +1.0u
3	Log +1.5u
4	Log +2.0u
m	Toggle AM basal as logged (in AM/PM mode)
e	Toggle PM basal as logged (in AM/PM mode)
b	Toggle daily basal (in once-per-day mode)
⌘↩	Log the custom-entry dose (when expanded)
Esc	Close the popover
⌘Q	Quit the app

Design philosophy

The discipline is just IOB, nothing else. Other diabetes apps that exist have all gone overboard — graphs, carb counting, BG correlation, predictions, dashboards, notifications, push reminders, social features. This one resists that pressure on purpose. If you want any of those features, fork it.

Why? Because in daily use, the question is almost always one of: "Did I just take insulin or did I imagine that?" A tool that answers that question in two clicks beats one that answers it in twelve clicks plus a dashboard.

Roadmap

See ROADMAP.md for planned future work, including iPhone/widget port, settings UI, HealthKit integration, and a separate-but-related blood glucose menubar app.

Acknowledgments

• LoopKit — the canonical open-source diabetes framework in the Apple ecosystem; source of the exponential pharmacokinetic model used here. Apache 2.0; attribution in NOTICE.
• KeyboardShortcuts by Sindre Sorhus — global hotkey registration with built-in rebind UI machinery. MIT.
• MenuBarExtraAccess by orchetect — programmatic control of MenuBarExtra's popover visibility, used here to let the global hotkey toggle the popover. MIT.

License

MIT.