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Starting Loop: Build

If you’ve decided to build Loop, the easiest method is to use the Build-Select script.  This script works for master and FreeAPS versions of Loop.  However, before you can do this, you must have already done the items on the Checklist.

Make sure to pay particular attention to the Cautions and Future Tasks sections that come after the Checklist. To be successful – you must not skip them.


  • Check that your Mac OS (or Virtual Mac) is the most current patch level of whichever OS you are running
    • If your phone has iOS 14.5 or later, your Mac needs Big Sur (11.x)
    • If your phone has an older iOS 14.4.2 or earlier, you can use Catalina
  • Check that your iPhone or iPod iOS is at the level needed to run the version you want to use (FreeAPS requires iOS 13)
  • Check that you have a compatible pump and CGM
  • Check that your radio-link is charged or has batteries (RileyLink, OrangeLink, or EmaLink)
  • Check that your version of Xcode is consistent with the iOS on your phone or install the correct version of Xcode
  • Check that your Apple Developer program subscription is valid and visit the site to make sure no new terms or conditions are pending acceptance
  • Check that you have a plan to deal with data for yourself, your doctor, or perhaps a caregiver
    • If this is for a child, consider how you are going to handle interactions with the school nurse and when/if/what do you need to add to the 504 plan
    • Make sure you are in a position to keep the school from taking away the RileyLink or Phone from your child

Build Loop

  • Plug in your phone and use the Build-Select to build the version you have selected
    • It may take a long time, but Xcode will always finish with a “Build Succeeded” or “Build Failed” message
    • If it failed – read the message – it may be as simple as your phone locked and needs to be unlocked
    • If it really failed, read the How To Ask For Build Help page
    • If it succeeded, at some point you will need to unplug your phone
    • You will get a message that Xcode lost connection with your phone – that is correct
    • Just walk away and admire your new app
  • Go to LoopDocs Setup App for instructions on how to set up your radio-link, pump, and CGM
    • These documents advise not to add Dexcom Share credentials when adding your CGM
    • Follow that suggestion – in fact, if you added your share credentials under the Transmitter setup screen, go back and delete your CGM and add the CGM back using just the Transmitter ID
  • After finishing the Set up App steps, continue to the LoopDocs Operate section and review the instructions on using your App
  • Leave Loop “Open” until you have adjusted your settings with Loop making predictions and suggestions, but not automatically enacting any insulin dosing recommendations


  • Your previous settings are probably wrong for Loop
    • Your settings were fine for manual pumping and manually correcting every few hours
    • Loop uses a model for carbs and insulin that updates once every 5 minutes based on your CGM readings
    • Start with Loop “Open” and check your settings until you have them close to your desired results
    • It is not uncommon to need a higher number for your ISF with Loop
  • Commit to checking in with the “source of truth” your are relying for information about the version of Loop that you are installing at least weekly to look for safety-related warnings. If you are not going to check in weekly, at a bare minimum, sign up for the Loop and Learn Newsletter, and read it when it shows up in your inbox.
  • Don’t be afraid to switch between closed-loop and open-loop often as you get your settings sorted out.
  • Overnights are often the first part of the day that people choose to run Closed Loop because, with proper settings, Loop will decrease or prevent low blood sugars and have you waking up in your target range. But, jump in the pool slowly.
  • You can use Loop as simply a Pump Controller (MMT) or PDM (Omnipod) to manually enter bolus amounts. When you run Loop “Open” it will make bolus recommendations that you can decide to manually administer.  As you grow confortable with those recommendations, you can start to run a “Closed” Loop and let Loop do the adjustments to your insulin dosing. Don’t think it is a race to be full-time Looping. You can Open and Close the Loop, watch, adjust, and learn.
  • In Open Loop, Loop will recommend temporary basals on the line below the HUD – you can “enact” or accept the recommendation by tapping on it.
  • And, always, if you have a dodgy CGM, Open Loop until stable CGM data is available. If the CGM is giving you bad data, Loop might make bad predictions. This is not a good idea. For example, if you restart your CGM sensors to extend their life, you know that the final days of that extended life can be dodgy.  While you are starting on Loop, you may decide not to do extended sensor sessions until you are confident of your new settings.

 Future Tasks

  • Data for Doctor:  Make a plan for how you will share your data with your doctors! The night before the appointment is too late.
  • Updates!  Make sure your Profile expiration date is on your calendar along with your Developer renewal date and your quarterly rebuild.


Please let us know with a post in Loop and Learn that you followed this Checklist and made it into Looping.  OR, if you don’t want to post in public, use the feedback form on this page to let us know.

We are all volunteers. We’d like to know if our hard work and passion putting together this information has helped people, or not.

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