CoreFast

CoreFast Privacy Policy

Last updated: October 21, 2026

CoreFast is an intermittent fasting tracker for iOS and Android, for adults 18 and over. This policy explains what data the app handles and, just as importantly, what it does not.

Summary

CoreFast keeps your fasting history, hydration logs, settings, and connected health readings on your device. It has no user accounts, advertising, or analytics SDKs. Optional Social Circles send end-to-end encrypted updates, limited to what you choose to share with each circle, through a short-lived relay so that circle's members can see them. Invites and exports leave your device only when you choose to copy or share them. When you scan a barcode, only its number is sent to Open Food Facts to look up the product; when you tap Search online, only the words you typed are sent to Open Food Facts to find matching products. Local weather on Today (off until you turn it on, which asks for location) sends your approximate location, rounded to about 10 km, to CoreFast's relay up to twice a day to fetch the forecast from Open-Meteo (see "Location"). CoreFast does not sell your data.

What CoreFast stores

CoreFast stores the following locally on your device only:

All of this except the crash log and the weather forecast is encrypted at rest (AES-256-GCM) using a key held in the iOS Keychain or Android Keystore, marked device-only so it is never copied to iCloud Keychain, Android auto-backup, or transferred between devices. The weather forecast is kept unencrypted in local app storage, outside backups, and deleted when you turn Local weather off, deny location, switch location off, when it runs out, or with your data. The crash log is kept unencrypted in local app storage — it exists only so the app can tell you about a crash (and let you share its technical details if you choose), and it is cleared as soon as you dismiss that message or delete your data. Your full local records are not uploaded to the Circles relay; only the optional encrypted updates described below are sent.

Social Circles and invitations (optional)

When you create or join a circle, CoreFast publishes updates that are end-to-end encrypted, so only that circle's members can read them. What each update carries depends on the choices you make for that circle:

Notes, proposals and a buddy pairing you set up are sent even when you share nothing else, since they exist only to be seen by the circle. Your streak is no longer sent. If the circle runs a group challenge, your updates also carry your result for each day of it (met, close, or missed); in a team hours challenge they carry your total fasted hours since the challenge began instead. For a water challenge the result comes from the water you logged in CoreFast, never from Apple Health or Health Connect: a day that included water imported from Health shares no mark (unknown) unless your CoreFast water alone met the goal, and Health amounts are never shared. A circle's host also publishes changes to the circle itself: a member they removed and that the circle was closed. When the host role is handed over, the former host keeps announcing who the current host is and when the role changed, for as long as that member remains host. When you leave a circle or delete all data, CoreFast sends one last encrypted update saying you left, so members take you off their list; it's skipped if you're offline. Circle members share an AES-256-GCM key and can read these updates. Anyone holding an invitation or that key can access the circle; this is not per-member identity verification, so anyone holding a circle's key could also act as its host, for example by closing the circle or removing members. Your full fasting history, your feelings history, and your connected health readings are not sent to the relay.

While you're in a circle, CoreFast occasionally syncs it in the background, even when the app is closed, so notes and start times can reach you. Your phone decides when (usually every few hours at most). These background updates are the same end-to-end encrypted updates described above, carrying only what you chose to share with each circle; nothing else is sent, and with no circles nothing is sent at all. You can turn this off in Settings → Circles → Background updates (or in your phone's settings).

The Cloudflare-hosted relay stores encrypted envelopes in short-lived buckets for up to 24 hours, with older envelopes also removed as buckets fill. Leaving a circle or deleting local data does not recall copies already received by members or immediately delete previously published envelopes. Members may retain their received copies.

Private invitation codes contain the circle key. Copying places the code on your clipboard; sharing sends it to the messaging service and recipients you select. Share only with trusted people. The shared invitation includes a tap-to-join link with the code after "#" (a URL fragment): browsers and apps never send that part to the invitation website or to link previews, so the website, which serves app-association files and instructions, never receives private codes. Tapping the link opens CoreFast with the code filled in; joining still takes your own tap. If CoreFast isn't installed, the link (with its code) can stay in your browser's history. The code is also in the message for pasting by hand.

Relay and invitation-host providers may process connection metadata such as IP address, request timing, and network-error reports under their own policies. Worker observability is disabled, but this does not establish that provider-level logs or reporting are absent.

Widgets, watch, and the Lock Screen

So they can show your fast at a glance, CoreFast keeps a small summary for its widgets and, if you use one, its watch app: your current plan, the current fast's start and end times, today's water, and your streak. On Android this summary is kept in the app's private storage, encrypted with a key held in the phone's secure key store (Android Keystore). If that key store fails on a device, the summary falls back to the app's private storage without that encryption, and CoreFast moves it back into encrypted storage as soon as the key store works again. On iOS it is kept in the app's App Group, shared only with CoreFast's widgets and watch app; it is not encrypted by CoreFast (only by iOS's own data protection), because widgets must read it without opening the app. It is sent to your paired watch directly by your phone's operating system (Apple's WatchConnectivity), never to CoreFast or any server.

With Apple Health connected, today's sleep, steps, active calories, latest glucose, resting heart rate and HRV are also sent from your iPhone directly to your Apple Watch (over Apple's WatchConnectivity) while CoreFast is open, shown there and kept only in memory — never stored on either device or sent to CoreFast or any server. They are not part of the summary above, so widgets never show them, and the watch hides them on its dimmed Always On face.

What shows on the Lock Screen: on iPhone you can add CoreFast's widget to the Lock Screen. While the phone is locked, its zone, plan, timer and caption ("left", "eat", "over") are hidden; the plain progress ring or bar still shows, without any numbers or words. If you turn on Live fasting status, your countdown also shows as an iPhone Live Activity or an Android notification. On iPhone, the Live Activity's Lock Screen banner (timer, zone, plan, end time and messages such as "You made it.") is marked private, so iOS hides it while the phone is locked; the Dynamic Island, shown while you use an unlocked phone, is not hidden. On Android, the live fasting notification is hidden from a locked phone and appears in the notification shade once it is unlocked, where anyone who can see your screen can see it. On Android 14 and later you can swipe it away; it stays hidden for the rest of that fast, and turning Live fasting status off and on again brings it back. On Android, reminders on the lock screen follow your phone's notification setting (for example, "hide sensitive content").

Siri, Shortcuts and quick controls: CoreFast's Siri answers ("How's my fast") are made on your iPhone from the same summary above, never from Apple Health. Starting or ending a fast or logging water from Siri, a Control, an Android app shortcut or the Quick Settings tile is saved on your phone in the same way as a widget tap; CoreFast sends none of it anywhere (how Apple handles your voice request to Siri is covered by Apple's own policy). If you add CoreFast's Fast control to your iPhone's Lock Screen, or its Quick Settings tile on Android, it shows whether you're fasting to anyone who can see your phone.

What CoreFast does not do

Apple Health and Android Health Connect (Optional Integration)

CoreFast provides an optional, opt-in integration with Apple Health (on iOS) and Android Health Connect (on Android). This integration is completely turned off by default.

What is read (with your consent)

When you enable health synchronization in CoreFast Settings, the app may read the following metrics directly from your device's health store:

What is written (with your consent)

Privacy and Data Handling Guarantees

Location

CoreFast only requests your device location if you choose the optional Sunrise to sunset fasting plan or allow it for Local weather (described below). The Sunrise to sunset plan needs it to calculate that day's sunrise and sunset. The app asks for a single, approximate location reading (not precise, continuous or background location; on Android approximate location is the only kind it can request, and on iOS it is the default) when you choose that plan or tap "Update my location" on it, and saves the resulting coordinates on-device, rounded to about a kilometre (two decimal places) — encrypted alongside your other settings, the same as everything else CoreFast stores — so the calculation can run each day without asking again. This Sunrise to sunset location is never transmitted to any server or shared with any third party. Choosing any other plan never requests or uses your location for fasting, and you can clear a saved location at any time via "Delete all local data" in Settings.

Seasons on Today (a gentle background tint, and a short greeting on festival days) use only the date and the Region your phone is set to, or a country you pick yourself in Settings (kept on your phone, and included in your backups with your other settings). They don't use your location, ask for no permission, and nothing about them leaves your phone. You can turn them off in Settings under Appearance. The weather part is described next.

Local weather (Settings › Appearance › Seasons & weather) is off until you turn it on, there or on Today's one-time "See today's weather here?" card (Turn on or Not now). Turning it on asks for location access on that tap; without it, Local weather stays off and nothing is sent. Once on, it checks the weather up to twice a day (when the forecast it has is 12 hours old), only while CoreFast is open, never in the background: it fetches the hourly forecast for the next three days, and your phone picks the current hour from it. CoreFast reads your approximate location and sends it, rounded to about 10 km (one decimal place), to CoreFast's relay; if no location is available in time, nothing is sent that day. If you deny location access, or switch location off on your phone, nothing is read or sent and Today shows the season instead. The relay asks Open-Meteo (open-meteo.com), a weather service, for the hourly forecast at the rounded place and passes back only the time, temperature, weather type, rainfall and day or night for each hour, and each day's sunrise and sunset times (so the sun and moon change at the right moment); Open-Meteo sees the relay, never your phone's IP address. The relay keeps the rounded place only with that place's forecast, for up to two days, never with anything that identifies you. Nothing about you or your fasting is sent, and every weather request (from the app to the relay, and from the relay to Open-Meteo) carries Do Not Track and Global Privacy Control signals, no cookies and no identifier. You can turn it off at any time in the same sheet.

Insights and on-device explanations

Insights such as "Your read" and "Your pattern" are worked out on your device from your own fasts and, if you connected it, your health data. On iPhones with Apple Intelligence, "Explain my week" can ask that model, on your phone, to put a short summary of these facts into words. Only a few numbers-only statements are given to it: no names, dates, notes or location. Nothing is sent to CoreFast, to us, or to any server for this, and it runs only when you tap. On other phones the same facts are shown as plain text. You can turn all of these insights off in Settings under Patterns in my data, or each one on its own. If a written explanation seems wrong, "Report a problem" hides it; you can also choose to email it to us from your own mail app, and nothing is sent unless you send that email.

Circle membership on this device

For each circle you join, CoreFast keeps a small note in your device's secure keychain of which circle member you are, so rejoining with the same code after an app reset brings you back as the same member. It stays on this device, is never sent anywhere, and is not carried to a new phone. It is removed when you leave that circle yourself, and every such note is removed when you use Delete all data (after a host removes you it is kept, so a rejoin is still recognized as the removed member). On iPhone, the keychain keeps it even if you delete the app, until you reinstall and use Delete all data.

Notifications

If you enable local reminders, or the evening reminder of the optional sugar-free challenge, CoreFast schedules notifications directly on your device using the operating system's notification framework. These reminders are generated and delivered entirely on-device; no reminder content is sent to or through any server.

Backup and export

CoreFast lets you export a backup as a plain JSON file, including circle memberships and shared keys if present. Backups also include your meals, meal favourites and scanned products, your feelings history, mutes, rest periods, milestone choice, circle notification settings and long-fast check-in answers. Backups leave out your health check answers, so a phone restored from one asks the health check again. From Insights › Trends, Share this week shows a picture card made on your device (which days this week had a fast end, and which days this month had one; no hours, goals or health readings), and opens your device's share sheet only when you tap Share; it is sent only if you choose a destination and send it. It also lets you share a plain-text health summary containing selected fasting, water, and available heart readings, and spreadsheet (CSV) files of your fasts, daily water (including how much came from Apple Health or Health Connect) and check-ins. A spreadsheet is created only when you choose to export one, and leaves your device only where you send it. These files are not encrypted: anyone who receives them can read them, and a backup's circle keys grant circle access. The destination and recipients are chosen through your device's share sheet. CoreFast does not upload these files automatically. Temporary backup and spreadsheet files are removed when you next open or return to the app (once a save in progress can finish) or export again.

Data deletion

You can delete your saved app data from Settings by choosing "Delete all local data." This removes your sessions, preferences, hydration history, meals, meal favourites and scanned products, challenges, circle memberships and keys, saved location and crash log from the device, clears the summary shown on widgets and your watch, and destroys the on-device state encryption key. This cannot be undone. It does not delete files you exported, messages you shared, copies retained by circle members, or still-unexpired relay envelopes. When you leave a circle or delete all data, CoreFast sends one last encrypted update saying you left, so members take you off their list; it's skipped if you're offline.

App updates

CoreFast does not check for or download updates by itself. Updates come only through the App Store and Google Play.

Children's privacy

CoreFast is intended only for adults 18 and over; its welcome guide says so and asks anyone younger not to use its fasting plans. CoreFast does not knowingly collect any information from anyone, including children. It has no accounts and keeps your records on your device; apart from files or emails you choose to share yourself, the only data that leaves it is the optional, end-to-end encrypted Circles updates described above, the barcode number sent to Open Food Facts when you scan a barcode, the words you typed sent to Open Food Facts when you tap Search online, and, while Local weather is on, an approximate location sent to CoreFast's relay for the forecast. The app includes a health and safety disclaimer and is not intended to provide medical advice to any user.

Changes to this policy

If CoreFast's data practices change in future versions, this policy will be updated accordingly and all handling of your data will remain opt-in only, with no automatic upload of your data to any server.

Contact

Questions about this policy can be sent to: corefast.support@icloud.com