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Build it yourself

You do not need to know how to code. If you can follow a recipe, you can do this. This guide holds your hand through every step — from making an Apple account to seeing the app on your own iPhone.

Take it slowly, one page at a time, in order. If a step doesn't work, don't worry — the Troubleshooting page covers the common snags.

Experimental — in development

faBolus can tell an insulin pump to deliver insulin, and it is not FDA-cleared. It's an open-source project for experimental use — you assume all responsibility. Please read Safety before you build anything.

What "building" means (in plain words)

This app isn't in the App Store. Instead, you copy its recipe (the "source code") onto a Mac, and a free Apple program called Xcode turns that recipe into the actual app and puts it on your iPhone. That's "building."

You do it once. Every so often you'll redo the last step to keep the app from expiring — that takes about a minute (see Keeping the app running).

You won't be typing commands (much)

This guide is click-and-point wherever possible: you'll use free apps like GitHub Desktop and Xcode, and Finder to move a file. There's just one short step that uses the Terminal, and it's written out word-for-word with plain-English explanations. Anything meant only for advanced users is tucked inside a "click to open" box you can ignore.

The whole process, start to finish

Four short chapters. The first three get the app on your iPhone; the last is an optional Garmin watch. The Garmin app is optional at build time — the phone app builds and runs fine on its own, and you can add the watch later.

  • 1 · Apple account

    Sign in with an Apple ID so you're allowed to put your own app on your phone.

    Start here

  • 2 · Install Xcode

    Get Apple's free app-building tool from the Mac App Store.

    Install Xcode

  • 3 · Put the app on your iPhone

    Download the code and press one button to install it.

    Build the app

  • 4 · Add a Garmin (Venu 3S)

    Build the Garmin remote for a Garmin Venu 3S — the one watch this app supports. Optional.

    Build for Garmin

Do you have everything?

You'll want all of these before you start (details on What you'll need):

  • A Mac computer (any recent one).
  • An iPhone (iOS 17 or newer) and a cable to plug it into the Mac.
  • An Apple ID — the same email/password you use for the App Store.
  • A Tandem t:slim X2 pump.
  • Optional: a Garmin Venu 3S.

How much time and money?

Free Apple account Paid account ($99/year)
Time for the first build About 1–2 hours, mostly waiting on downloads About 1–2 hours
App keeps working for 7 days, then you redo one step 1 year
Widgets Can be fiddly Work smoothly

Which should I pick?

Start free — it costs nothing and works. If you end up using the app regularly, the $99/year account means you only re-install once a year instead of weekly, and the widgets behave better. You can switch to paid later without redoing anything.

Ready? Go to Step 1 · Apple account. Just follow each page in order and you'll be fine.