Policy · Privacy

Your data stays on your phone.

Last updated 2026-04-26

This is the privacy policy for the HackDiet iPhone application, published on the Apple App Store. It does not cover the separate self-hosted web application at hackdiet.lambda-m.nl/webapp, which is private to friends and family of the developer and operates under its own (verbal, but consistent with this) commitments.

Plain-English summary

HackDiet does not collect any data about you. Everything you log stays on your iPhone. There are no servers we send anything to, no analytics, no advertising, no third-party SDKs. If you uninstall the app the data is gone with it (unless you have iOS device backup enabled, in which case it lives in your iCloud backup, encrypted under your Apple ID).

What HackDiet stores

The app stores the following on your device only:

• The body weight values you log, with the dates they were logged on.
• The daily comments, "rung" values, and flags you optionally attach to each day.
• Your preferences: display unit (kilograms / pounds / stones), goal weight, daily calorie balance, etc.

This data lives in a SQLite database file inside the app's private container at Library/Application Support/hackdiet/hackdiet.sqlite. It never leaves your device through any code path that HackDiet controls.

What HackDiet does NOT collect

• No name, email, phone number, or any identifier of you.
• No device identifier, advertising identifier, IDFA, or analytics token.
• No usage statistics, crash reports, or telemetry of any kind.
• No location data.
• No data from other apps or sources except Apple Health, and only with your explicit per-app permission (see below).

Network access

HackDiet makes zero outbound network connections. The shipped binary contains no HTTP client code path, no analytics SDK, no crash reporter that calls home, no advertising. You can verify this by running the app in airplane mode — every feature works.

The app does include links to external websites in its About screen. When you tap one of those links, iOS opens it in Safari, which is governed by Safari's privacy settings, not HackDiet's.

Apple Health integration (optional, off by default)

HackDiet offers two distinct Apple Health features in Settings, both opt-in:

1. Sync with Apple Health — ongoing, both directions. New weights from Apple Health fill days you haven't logged in HackDiet; weights you log in HackDiet are written back to Apple Health. Asks for Read and Write permission.
2. Import history from Apple Health — one-shot, read-only. Pulls existing weight history into HackDiet without enabling sync. Asks for Read permission only.

The data flow has clear, predictable rules: Apple Health fills empty days only, days you type in HackDiet are never overwritten, and if Apple Health has several weights on the same day HackDiet uses the latest one. The full policy — including how to reset HackDiet's Apple Health data without affecting any other Health metric — lives at Apple Health & HackDiet.

This integration uses Apple's HealthKit framework and is governed by Apple's privacy policy as well as your iOS Health permission settings. HackDiet only reads and writes Body Mass — it cannot see and cannot affect step counts, sleep, heart rate, or any other Apple Health metric. HackDiet never sees your Health data leave your phone.

You can turn either feature off at any time in HackDiet's Settings, and revoke the underlying permission in iOS Settings › Privacy & Security › Health › HackDiet.

iCloud Backup (optional, controlled by you)

If you have iCloud Backup enabled on your iPhone (most users do by default), Apple includes the HackDiet database in your encrypted device backup. This is the same mechanism that backs up your photos, messages, and other apps. Apple operates this; HackDiet doesn't see or control it.

If you restore your iPhone from a backup, your HackDiet history comes with it.

Notifications (optional, off by default)

If you turn on "Gentle log reminders" in Settings, HackDiet schedules local notifications on your device using iOS's UserNotifications framework. These are scheduled and delivered entirely on-device — nothing about them goes through Apple's push notification service or any external server.

Data export

You can export your full data as an open, portable XML file at any time via Settings → Export Data. The file ends up wherever you choose to save it (Files, AirDrop, email, etc.). HackDiet doesn't keep a copy of the export.

Data deletion

To delete HackDiet's own data: Settings › Erase all data, or uninstall the app entirely. Either removes the local SQLite database and any cached state.

For the Apple Health side, the Erase confirmation gives you a choice:

• Erase only — HackDiet's local data is removed; weights HackDiet wrote to Apple Health stay in Apple Health.
• Erase + clear Health — HackDiet's local data AND every body-mass sample HackDiet ever wrote to Apple Health are removed. Other Health metrics (steps, sleep, heart rate, etc.) are untouched.

You can also remove HackDiet's Apple Health data without erasing the local app, via the iOS Health app: Sources › HackDiet › "Delete All Data from this Source." This is an iOS feature; it only ever touches data the named source wrote.

Children

HackDiet doesn't collect data, so it doesn't collect data from children either. The app's age rating in the App Store is 17+ to be careful around eating-disorder topics; if you are younger and want to track your weight, please consider whether that is something you want to do, and talk to a parent or doctor if you are not sure.

Changes to this policy

If this policy ever changes, the updated version will appear at the same URL with a new "Last updated" date. Material changes will also be noted in an in-app banner.

Legal

Data controller

The publisher of HackDiet for iOS is the Dutch Besloten Vennootschap (BV) responsible for lambda-m.nl, registered with the Dutch Kamer van Koophandel (KvK). Trader-disclosure information per EU Digital Services Act Article 31 is published in the App Store listing's "App Privacy" + "Information" sections.

Because HackDiet collects no personal data and processes none on any server, the BV holds no records about you. There is no GDPR data subject request to process — there is no data.

California (CCPA / CPRA)

HackDiet does not collect, "share", or "sell" personal information as those terms are defined in the California Consumer Privacy Act / California Privacy Rights Act. The CCPA's revenue + scale thresholds are not met by the publisher in any case. This notice exists to defuse automated privacy-policy scanners.

Apple App Store privacy questionnaire

Per Apple's own definition, data that is "collected solely on the end-user's device and is not sent off the device in a way that could identify the user or device" is not "collected" for App Store privacy purposes. HealthKit data read or written locally by HackDiet without transmission therefore correctly reports as "Data Not Collected" in the App Store privacy nutrition label.

Contact

For questions: support@lambda-m.nl. This is the only email address associated with HackDiet, and it is monitored personally.

HackDiet is an independent app. It is not affiliated with Apple Inc.