Gutline
Contents
Privacy Policy for the Gutline app
Last updated: 10 October 2026
*The German version of this document is the authoritative one. This is a convenience translation, provided because Apple links the privacy policy from every storefront.*
The short version
Gutline is a diary for digestive symptoms. It stores everything you enter on your iPhone and nowhere else. There is no server of ours, no account, no sign-in, no sync, and no analytics or advertising services.
What you enter is health data. Symptoms, stool type, blood in stool, medication and meals belong to the special categories of personal data under Art. 9 GDPR. So we say it plainly: this data stays on your device. The publisher never receives it, cannot see it and has no way to get it.
Three things leave your phone anyway, and they are at the top of this page rather than buried in it:
- Purchases. The "Gutline Pro" subscription is handled entirely by Apple. The app asks Apple for the prices and whether a valid subscription exists. Apple therefore learns that this app is being used on this device.
- Your device backup. If you have iCloud Backup or a computer backup switched on, Gutline is part of that backup like every other app. A copy of your diary then sits with Apple, or on your computer. You control this, not the app.
- This website. The "Privacy" and "Terms" links in the app open your browser and fetch mk-sd.com. Your IP address is then transmitted to the host.
And a fourth, which you trigger yourself: when you pass a report or a CSV file on through the iOS share sheet, you alone decide where it goes.
Details on all of this are in section 6.
1. Controller
Maximilian Kuchlbauer
Flurstr. 1
84524 Neuötting
Germany
Email: maximilian.kuchlbauer@gmail.com
No data protection officer has been appointed.
2. What this app technically does
This section does not describe what would be desirable. It describes what was checked in the app's source code (Sources and GutlineCore, as of version 1.0.2).
- No server of ours, no account, no sync. The source contains no network call to a server of the publisher or of any third party. It was searched for
URLSession,URLRequest,WKWebView,SFSafariViewControllerand for analytics, crash and advertising libraries (among others Firebase, Crashlytics, Sentry, Amplitude, Mixpanel, PostHog, RevenueCat, Adjust, AppsFlyer). None of these terms appears in the code. The Swift packageGutlineCore, which holds the calculation rules, has no dependencies. - Local storage in files. Your diary is a file
entries.json, your food and habit log isfood.json, and your medication and therapy plan istherapy.json, in the app's "Application Support" directory on the device. Photos are JPEG files in thePhotossubfolder of the same directory. The app does not encrypt these files itself; the protections of iOS apply (section 10). - Settings (appearance, left-handed layout, reminder time, which symptoms you track and which you created yourself, hidden tags, the answers given in the introduction, whether the lock is on) are stored in the app's
UserDefaultson the device. - Photos. You can attach a photo from your library to an entry (Gutline Pro). The app uses the iOS photo picker (
PhotosPicker). It therefore does not request access to your whole library and sees only the image you choose. The app has no access to the camera. The chosen image is stored as a copy inside the app and uploaded nowhere. The photo appears neither in the PDF report nor in the CSV file. - Face ID and device passcode. The optional lock (Gutline Pro) uses Apple's
LocalAuthenticationframework. Biometric data never leaves the Secure Enclave and is never seen by the app; the app only learns whether the system accepted the unlock. The app stores nothing for this except the setting that the lock is on. The only permission text set in the project configuration is the one for Face ID (NSFaceIDUsageDescription). - Local notifications. The app can show a daily reminder and, if you choose so when starting a trial, a reminder two days before the trial ends. Both are local notifications triggered by your device itself. There are no push notifications through a server. iOS asks for the permission only when you switch on the reminder or choose the trial reminder, not at first launch.
- Export. The app generates a PDF report (the last 90 days) and a CSV file of all entries. Both files are kept ready in the app's temporary folder so that sharing is instant, and this already happens when you open Settings or the Today screen, not only when you tap share. They leave the device only if you pass them on through the iOS share sheet. iOS cleans the temporary folder itself, at a time the app does not control.
- No advertising ID, no tracking. The app reads neither
advertisingIdentifiernoridentifierForVendorand does not ask for App Tracking Transparency. No tracking across apps or websites takes place. The app's privacy manifest (PrivacyInfo.xcprivacy) declaresNSPrivacyTrackingas false, lists no tracking domains and no collected data types. - No access to Apple Health, location, contacts or calendar. The source contains no call into these frameworks, and the matching permission texts are not set.
- No entitlements file. The project contains no
.entitlementsfile, so none for iCloud, CloudKit or an app group either. - The privacy manifest names two system interfaces:
UserDefaults(reason CA92.1, the app's own settings) and file timestamps (reason C617.1, access to files in the app's own container). Both stay on the device.
3. What data is processed
| Category | Examples | Purpose | Where it is stored |
|---|---|---|---|
| Diary entries (health data) | time, severity 0 to 10, stool type on the Bristol scale, urgency, blood, medication taken, symptoms with level, tags and triggers, note | Core function: recording and reviewing symptoms | Locally on the device only (entries.json) |
| Photos (health data if they show your body) | one image per entry, if you attach one | Attaching a picture to an entry | Locally on the device only (Photos) |
| Food and habit log | meal, drink or habit with time and your reaction afterwards | Core function: reaction check | Locally on the device only (food.json) |
| Medication and therapy plan | name, dose as you typed it, time of day, taken ticks | Core function: ticking off intake and comparing with symptoms | Locally on the device only (therapy.json) |
| Settings | appearance, reminder time, tracked symptoms, answers in the introduction (including goals you typed yourself) | Personalising the app | Locally on the device only (UserDefaults) |
| Purchase and subscription status | product identifier, purchase state, subscription period; only the fact that access once existed is remembered locally | Unlocking Gutline Pro | At purchase, with Apple. The app reads back from Apple only whether a valid entitlement exists |
The app asks neither for your name nor for an email address nor for a date of birth. The PDF report carries no name.
This data is health data within the meaning of Art. 4(15) and Art. 9 GDPR. The publisher does not process it in any case, because it never reaches him.
4. Legal bases
- Diary, photos, logs, plan and settings on the device: Storage takes place solely in your own terminal equipment and serves only the function of the app that you want. The publisher has no access to this data. In our assessment, no processing by the publisher takes place for which he would need a legal basis under Art. 6 and an exception under Art. 9(2) GDPR. Where one nevertheless sees processing by the publisher in it, it rests on Art. 6(1)(b) GDPR (performance of the contract for using the app) and on your explicit act of entering the data into the app yourself (Art. 9(2)(a) GDPR).
- Storage on your device (section 25 TDDDG): Storing your entries in the app is strictly necessary for the function you expressly request, keeping and reviewing your diary. It falls under the exception in section 25(2) no. 2 TDDDG and needs no consent. Nothing is stored on your device for any other purpose, in particular reach measurement or advertising.
- Purchases: Art. 6(1)(b) GDPR. The purchase contract for the subscription is formed between you and Apple, not between you and the publisher of this app.
- Visiting this website: Art. 6(1)(f) GDPR (legitimate interest in delivering the page without technical error and securely).
5. Recipients
Beyond the cases named in section 6, no data is passed to third parties. There are no processors for app data, no analytics, advertising or marketing providers, and no sale or exchange of data. A sale would be technically impossible anyway, because the publisher has nothing to sell.
6. What leaves your phone anyway
The statement "your data does not leave your phone" describes what the app does: Gutline sends your diary to no one. It does not describe what Apple and you yourself do with the device. These paths are named for completeness.
6.1 Purchases through the App Store (StoreKit)
Gutline Pro is a subscription in three durations, weekly, monthly and yearly (com.mksd.gutline.pro.weekly, .monthly, .yearly), handled through Apple's in-app purchase.
What the app does: at launch it checks with Apple whether a valid entitlement exists, and loads the products' descriptions and prices. It also asks Apple whether you are still eligible for a free trial. At purchase, iOS opens Apple's own purchase sheet. When you tap "Restore purchases", the app asks Apple to refresh the device's purchase history.
What the publisher learns: only whether a valid entitlement exists on this device. He receives from Apple neither your name, your email address, your address, your payment details, nor any identifier with which a purchase could be attributed to a person. In App Store Connect he has only aggregated sales and subscription statistics.
What Apple processes: Apple Inc. or Apple Distribution International Ltd. processes the purchase, payment and device information **as an independent controller**, not as a processor of the publisher of this app. Apple's own privacy policy applies (https://www.apple.com/legal/privacy/en-ww/). The publisher of this app has no influence on it. Rights relating to purchase data are to be asserted against Apple. Your diary data takes no part in this process.
6.2 Backup of your device
Gutline keeps its files in the app's normal data directory. iOS includes this directory in the device backup, and the app does not exclude it. In practice this means:
- If iCloud Backup is on, a copy of your diary, photos, logs and plan sits in your device's backup on Apple's servers. Apple encrypts backups in transit and in storage, and end to end with "Advanced Data Protection" switched on. Those are Apple's statements, not measurements by the publisher.
- If you back your iPhone up to a computer instead, the copy sits there.
- If you make no backup, none of this leaves your device.
The device backup is a general iOS function that affects every app. You control it in iOS Settings under your name, iCloud, iCloud Backup. There the backup can be switched off entirely, and iOS also lets you exclude individual apps.
Apple is responsible for the backup, not the publisher of this app. He has no access to your backup and can neither see whether one exists nor what is in it.
6.3 Sharing a report or a CSV file
With Gutline Pro you can pass a PDF report and a CSV file on through the iOS share sheet, for example by AirDrop, Messages, email or to a cloud folder. Both contain health data from your diary: the report holds summaries and every entry of the last 90 days with notes, the CSV file all entries with notes. Where the file goes afterwards is your decision and your action. The publisher is not involved and receives no copy. From the moment you pass it on, the rules of the app or service you give it to apply.
6.4 Visiting this website
The "Privacy" and "Terms" links in the app (in Settings and on the purchase screen) open the browser. Visiting mk-sd.com is an ordinary website visit. The "Support" link in Settings opens your mail app with an empty message to support@mk-sd.com; only what you send is sent.
This site is delivered through Cloudflare, Inc. Cloudflare processes technically necessary connection data, in particular the IP address, the time of the request, the requested address and the browser identifier, to deliver the page and to fend off attacks. Cloudflare acts as the publisher's processor under Art. 28 GDPR. A transfer to the USA may take place; it is safeguarded by the EU Commission's standard contractual clauses and Cloudflare's certification under the EU-US Data Privacy Framework. Details about the website are in the privacy notice at https://mk-sd.com/en/privacy
6.5 When you write to the publisher
This is the only case in which the publisher actually processes personal data of yours, which is why it is stated here expressly.
If you write through the contact form on mk-sd.com or to maximilian.kuchlbauer@gmail.com or support@mk-sd.com, the publisher processes your email address and the content of your message in order to answer it. The legal basis is Art. 6(1)(b) GDPR where it is about the app or your subscription, otherwise Art. 6(1)(f) GDPR (legitimate interest in answering enquiries). Please do not put health data into your message that we do not need for the answer; a screenshot of your entries is not needed for support. The message is deleted once it is dealt with and no retention duty stands in the way.
7. Retention
Your diary, photos, logs and plan stay on your device until you delete them. How:
- Single entries you delete in the app by swiping or from the context menu. The entry's photo is deleted with it.
- "Delete all entries" in Settings removes all diary entries and all photos. It does not remove the food and habit log, the medication and therapy plan or your settings. You delete those one by one in the app (Settings, "Your additions"; the food log and the plan from their own screens).
- Everything at once you delete by uninstalling the app. iOS then removes the app's entire data from the device.
Important, because it would otherwise surprise you: a backup that has already been made is not touched by this. As long as a backup exists, the copy in it exists too, until you delete or overwrite the backup yourself. Likewise a file you shared stays wherever you put it.
No retention period arises at the publisher, because nothing is stored there.
8. Your rights
Under the GDPR you have the rights of access (Art. 15), rectification (Art. 16), erasure (Art. 17), restriction of processing (Art. 18), data portability (Art. 20) and objection (Art. 21).
How they work out in practice for this app:
- Access (Art. 15): The publisher holds no data about you from the app and therefore cannot give access to your diary. A request is answered with exactly that. What the app knows about you you can see completely in the app itself. If you have written to the publisher, the right of access relates to that correspondence (section 6.5).
- Rectification (Art. 16): directly in the app, by editing an entry.
- Erasure (Art. 17): in the app as described in section 7, or by uninstalling the app. There is no copy at the publisher that would need to be deleted separately. For backups already made, see section 7.
- Data portability (Art. 20): With Gutline Pro you export all entries as a CSV file, a common machine-readable format. The CSV contains diary entries; photos, the food log and the therapy plan are not in it.
- Objection and restriction (Art. 18, 21): Because no processing of your diary data takes place at the publisher, these rights come to nothing against him. You can end the processing at any time by no longer using the app or by uninstalling it.
- Withdrawing consent (Art. 7(3)): The app obtains no consent for the publisher because he receives no data. You can withdraw the system permission for notifications at any time in iOS Settings, and Face ID for the app too. You cancel purchases in the settings of your Apple account; you switch off your device backup in iOS Settings (section 6.2).
- Purchase data: to be asserted against Apple, see section 6.1.
- Right to lodge a complaint (Art. 77): You may complain to a data protection supervisory authority, in particular the one responsible for your place of residence. Responsible for the publisher is the Bavarian State Office for Data Protection Supervision (Bayerisches Landesamt für Datenschutzaufsicht), Promenade 18, 91522 Ansbach, Germany.
For questions: maximilian.kuchlbauer@gmail.com
9. Children
The app is not aimed at children. It collects no data for which consent under Art. 8 GDPR would have to be obtained. Buying the subscription runs through the Apple account and is subject to Apple's rules on Family Sharing and Ask to Buy.
10. Data security
Because all data stays on the device, the protections of iOS apply: the app sandbox, file system encryption and the device passcode. The app does not encrypt its files additionally. The optional lock with Face ID or passcode is a screen guard against others who hold your unlocked phone: it locks the app's interface as soon as the app leaves the foreground and does not encrypt any file. The publisher takes no additional server-side measures, because he runs no servers for app data. The pages on mk-sd.com are delivered over HTTPS only.
11. Automated decisions
There is no automated decision-making and no profiling within the meaning of Art. 22 GDPR. Averages, trends and comparisons, such as which tags occur more often on days with higher severity, are calculation rules over your own entries, run on your device, without legal or similarly significant effect. They are neither a diagnosis nor an indication of a cause.
12. Medical notice
Gutline records what you enter and shows it back to you. **It is not a medical device and provides no medical advice, diagnosis or treatment.** For questions about your health, always consult a qualified doctor. Blood in the stool is a reason to seek medical advice; the app does not evaluate it.
13. Changes to this policy
This policy describes the state of the app on the date above. It is changed before a function ships that alters it. That applies in particular to:
- an iCloud or CloudKit sync (the entries would then leave the device by design and not only in a backup),
- a connection to Apple Health,
- analytics, crash reporting or advertising services of any kind (the statement "no tracking" would then no longer be correct),
- an account or a server of the publisher.
The current version is at https://mk-sd.com/en/gutline/privacy
*This policy describes the data processing checked in the source code of the Gutline app as of 10 October 2026. It is not legal advice and does not replace a review by a lawyer.*