Privacy Policy for the "Mahjong" App
Last updated: July 2026
1. Who is responsible
Joe Waldow
Hasenbusch 52
25335 Elmshorn, Germany
Email: joe.waldow@me.com
2. The short version
Mahjong is built to be deliberately data-minimal:
- No user account: The app works without any registration.
- No ads and no tracking: There are no advertising SDKs, we do not build profiles about you, we do not follow you across other apps or websites, and we never share anything with ad networks or data brokers.
- Your game progress stays yours: It lives on your device and, if you use iCloud, in your personal iCloud account. We have no access to it.
- We use two service providers: one for purchase processing (RevenueCat) and one for a small set of fully anonymous usage statistics (TelemetryDeck, a German company). Details are below.
3. Game progress and settings
Your progress, stars, statistics, and settings are stored locally on your device. If you have iCloud enabled, Apple syncs this data between your devices (iPhone, iPad, Mac) via the iCloud key-value store. This data lives exclusively in your personal iCloud account with Apple; we can neither see nor analyze it. Apple's privacy policy applies: https://www.apple.com/legal/privacy/
4. Purchases (Full Version)
The app offers a single one-time in-app purchase ("Full Version").
Apple: Payment is handled exclusively by Apple through the App Store. We never receive your payment details (such as credit card numbers) or your name.
RevenueCat: To process and validate the purchase (for example, so the full version can be restored after you switch devices), we use RevenueCat, Inc. (California, USA) as a data processor. The following is processed:
- a randomly generated, anonymous user identifier (no name, no email address),
- your purchase history within this app (product purchased, time, price region),
- technical details such as device type, operating system version, and language setting.
This data is used solely for purchase processing, restoring purchases, and fraud prevention, plus aggregate revenue statistics. It is not linked to your identity and is not used for advertising or tracking.
The legal basis is Art. 6(1)(b) GDPR (performance of a contract) and Art. 6(1)(f) GDPR (legitimate interest in fraud prevention and reliable purchase restoration). Transfers to the USA are based on the EU Standard Contractual Clauses and/or the EU-US Data Privacy Framework. More information: https://www.revenuecat.com/privacy
5. Game Center (optional)
If you use Apple's Game Center (leaderboards, achievements, comparing with friends), Apple processes your Game Center nickname and your submitted results (such as best times and stars). Participation is voluntary: the app explicitly asks before submitting times for comparison, and you can turn this off in Settings at any time. Apple Game Center's privacy terms apply: https://www.apple.com/legal/privacy/
6. Challenge links
You can challenge friends to a duel on the same board via a link. Such links contain only the level identifier and the target time, but no personal data.
7. Anonymous usage statistics (TelemetryDeck)
To improve the app, we collect a small number of anonymous usage statistics through TelemetryDeck, a service operated by TelemetryDeck GmbH (Augsburg, Germany). Specifically, we only learn:
- which age group was chosen on first launch (youth / adult / senior), because it drives the legibility defaults,
- whether the introduction was completed or skipped, and which category was opened first,
- that the purchase screen was shown or a purchase was completed,
- plus technical basics such as app version, operating system version, device model, and language.
TelemetryDeck specializes in privacy-friendly statistics: device identifiers are anonymized on your device using a salted, irreversible hashing scheme. No advertising ID is used, IP addresses are not stored, and neither we nor TelemetryDeck can attribute the data to a person. The statistics exist only in aggregate form ("how many", never "who").
The legal basis is Art. 6(1)(f) GDPR (legitimate interest in improving the app). Because the data is anonymized, no consent is required. More information: https://telemetrydeck.com/privacy
8. What we do NOT do
- We do not show ads.
- We do not track you: no following you across other apps or websites, no advertising ID, no sharing with ad networks or data brokers.
- We do not sell data, and we do not share data with third parties (apart from the two processors named above).
- We do not collect location data, contacts, photos, or any other sensitive data.
9. Retention
The anonymous purchase data at RevenueCat is stored for as long as needed to provide the full version. The anonymous usage statistics exist only in aggregate form and cannot be attributed to a person. You delete local game data by deleting the app; iCloud data can be removed in your device's iCloud settings.
10. Your rights
Under the GDPR you have the right of access (Art. 15), rectification (Art. 16), erasure (Art. 17), restriction of processing (Art. 18), data portability (Art. 20), and objection (Art. 21). To exercise these rights, contact the email address above. You also have the right to lodge a complaint with a data protection supervisory authority.
Because purchases are processed under an anonymous identifier only, we may be unable to match you to individual records; in that case we will assist you as far as possible (Art. 11 GDPR).
11. Children
The app is aimed at a general audience and does not collect any data beyond what is described above. That applies to children as well.
12. Changes
We will update this privacy policy if the app or the legal situation changes. The current version is always available at https://waldow.app/privacy-mahjong