Klar

An iOS app for people who want to cut down on their substance use without quitting. No account, no server, no analytics — the data never leaves the phone.

German UI, German market first. Not shipped: no App Store release and no external users yet. All fifteen screens, light and dark, are in docs/screenshots/ — every number in them comes from the sample dataset in examples/, nothing is mocked up.

Why this is not a tracker

Logging on its own barely moves consumption. That is the starting point rather than an afterthought: across the ecological momentary assessment literature (Shiffman, 2009) and a randomised diary experiment (Buu et al., 2020), self-monitoring produces little to no lasting change, and the authors of the latter attribute that directly to the absence of any feedback layer.

The one piece of app-level component evidence is a 2⁵-factorial trial of the Drink Less app (Crane et al., 2018). It found no significant main effect for any individual module, but a significant interaction between self-monitoring and action planning. So Klar builds those two as a pair: every entry feeds a quota and a weekly review, and the if-then plan sits on the same screen as the log.

The same evidence decided what to leave out. Normative feedback ("you drink less than 70% of users") has meta-analytic support and is deliberately absent, because no valid norm data exists for illegal substances and a user below the average reads it as permission.

The full argument, the design principles derived from it, and an explicit section on the limits of the evidence are in docs/klar-mvp-konzept.md.

What it does

Entry logging with context tags, per-substance monthly quotas, if-then action plans with check-ins, a three-step weekly review, calendar and trend history, behaviour substitution prompts, and a craving SOS screen with attributed content from established organisations.

Architecture

Two pieces, split along a line that is enforced rather than aspirational:

• Klar/ — the Xcode project. SwiftUI views, SwiftData persistence, app lifecycle, design system, app lock.
• Packages/KlarCore/ — the domain logic as a local Swift package. Quota calculation, statistics, plan sentences, logical-day handling.

Every file in KlarCore imports Foundation and nothing else. No SwiftData, no UIKit, no SwiftUI. That is what makes the interesting logic testable in milliseconds on a plain Mac, with no simulator and no Xcode in the loop:

swift test --package-path Packages/KlarCore   # 23 tests, ~8 ms

The package declares .iOS(.v17) while the app targets 26.5. The core is deliberately the more portable half.

Alongside those: docs/ holds the concept notes, pitch material and screenshots, examples/ an importable sample dataset covering every screen, regenerated by tools/, and web/ the landing page.

Privacy, as something checkable

"Privacy-first" is easy to write, so here is what it means in the repo:

• No networking code exists. There is no URLSession, no CloudKit and no analytics SDK anywhere in the sources.
• PrivacyInfo.xcprivacy declares no tracking and an empty set of collected data types.
• The store is entitled NSFileProtectionComplete and excluded from iCloud backup, so the data cannot leave the device through a backup either.
• Optional Face ID lock, plus a snapshot shield that covers the UI in the app switcher.

A decision worth naming

A day does not end at midnight. Someone logging a drink at 02:00 means the night that started yesterday, and a quota rolling over at 00:00 would split one evening across two months.

LogicalDay therefore puts the boundary at 05:00 and does every comparison in an explicit timezone. The cost is a window between midnight and 05:00 where the date the app shows disagrees with the phone's clock. Rather than hide that, isBeforeCutoff exists so the UI can say which day it means. A silent contradiction there would be worse than an explanation.

Running it

Xcode 26.6+, iOS 26.5+. Open Klar/Klar.xcodeproj, select the Klar scheme and run — there is nothing to configure, no API keys and no backend to point at. To get the screens populated, import examples/klar-beispieldaten.json from Einstellungen → Daten. KlarCore on its own needs only a Swift toolchain.

Limitations

Almost all the cited evidence comes from alcohol and tobacco research. Applying it to other substances is a plausible extrapolation, not an established result, and the concept document says so at more length. This is not a medical product and makes no therapeutic claim, and there is no evaluation in its own context yet. The UI is German only, and there is no CI.

License

MIT, see LICENSE.