Building Rhythmiva — Private Cycle Tracking App for iOS and Android
Rhythmiva is a private cycle tracking application I developed for iOS and Android.
The app is designed to help users track period dates, symptoms, mood, sleep, pain, energy, temperature, medication, notes, and personal patterns with calm, clear tools. Rhythmiva can be used locally without an account, while optional Rhythmiva Cloud adds secure sync, browser access, restore support, AI insights, and selected sharing features.
The goal of this project was to build a privacy-first personal tracking product that feels simple for daily use, but still includes deeper tools for reviewing patterns, preparing appointment summaries, and keeping data available across devices when the user chooses to enable cloud sync.
Project Details
Role: Owner / Mobile App Developer
Platforms: iOS and Android
App Type: Private Cycle Tracking App
iOS Stack: SwiftUI, Swift, local storage, biometric protection, Rhythmiva API, privacy manifest
Android Stack: Kotlin, Jetpack Compose, local JSON storage, biometric protection, reminders, Rhythmiva API
Focus: Cycle tracking, daily logs, privacy controls, cloud sync, AI insights, appointment-ready reports
App Store: https://apps.apple.com/us/app/rhythmiva/id6773687000
Google Play: https://play.google.com/store/apps/details?id=com.kolesnyk.rhythmiva&hl=en
What I Developed
I designed and developed Rhythmiva as a complete cross-platform mobile application for iOS and Android.
The app includes a private local tracking mode, optional Rhythmiva Cloud account support, daily symptom logging, cycle calendar, attachment handling, AI assistant workflow, privacy controls, app lock, reminders, report generation, sharing links, and account deletion from inside the app.
A key part of the project was keeping the experience clear and calm. Cycle tracking apps handle sensitive personal information, so the product needed to feel trustworthy, understandable, and respectful of user control.
Cross-Platform Development
Rhythmiva was developed for both iOS and Android using native technologies.
The iOS version was built with SwiftUI and Swift. It includes the main app interface, onboarding, cycle models, local storage, cloud API service, biometric lock, AI assistant, calendar, daily log, insights, doctor report, privacy screens, and cloud account workflow.
The Android version was built with Kotlin and Jetpack Compose. It includes a matching product structure with local data storage, JSON mapping, cycle calculations, cloud sync bridge, biometric lock, reminders, AI history, export, reports, and privacy controls.
Building both platforms required more than copying the same idea twice. The challenge was to keep the user experience consistent while implementing each version in its own native mobile ecosystem.
Local-First Tracking
One of the most important product decisions was making Rhythmiva usable without an account.
Users can start tracking locally on their device and keep their private data offline if they prefer. This makes the app useful for people who want personal tracking without immediately creating a cloud account or sending data to a server.
The local tracking system supports:
- Period dates
- Flow level
- Pain level
- Symptoms
- Mood
- Energy
- Sleep
- Temperature
- Medication
- Private notes
- Attachments and photos
This local-first design gives users control over how much they want to store, sync, or share.
Cycle Calendar and Daily Logs
Rhythmiva includes a cycle calendar and daily log system.
The calendar helps users review logged period dates and estimated dates. The daily log allows users to record symptoms, mood, sleep, pain, energy, temperature, medication, and personal notes.
The app is designed to support everyday use. A user can quickly add a log for the day, review previous entries, and look back at patterns over time.
The calendar and daily log work together: period entries provide the cycle structure, while daily logs provide the details that help the user understand how they felt during different days of the cycle.
Optional Rhythmiva Cloud
Rhythmiva Cloud is optional.
Users can continue using the app locally, or they can sign in when they want cross-device sync, restore support, and access to a private web cloud cabinet.
Cloud support was implemented as an extension of the local-first workflow rather than a requirement. This means the app remains useful without an account, but becomes more powerful when the user wants data synchronization and browser access.
The cloud workflow includes:
- Account sign in and registration
- Secure sync with the mobile app
- Cross-device restore support
- Optional automatic sync
- Cloud session handling
- Account deletion from inside the app
- Local data preservation when cloud account state changes
This structure gives users flexibility while keeping account-based features clearly optional.
AI Insights
I added an optional AI assistant for educational pattern explanations.
The AI workflow is designed to help users ask questions about logged patterns, generate educational explanations, and prepare better summaries for appointments. The app also supports photo questions when the user chooses to use them.
Because this is a sensitive category, the AI assistant is positioned carefully. It is not a diagnostic system, not a treatment tool, and not a replacement for professional medical care. The AI experience is designed for education, pattern explanation, and appointment preparation.
The app also includes medical information source links in the AI answer experience, and the AI flow is built around explicit user consent before cloud AI analysis is used.
Appointment-Ready Summaries
Rhythmiva includes appointment-ready summaries for healthcare visits.
The goal is to help users bring clearer information to a professional appointment. Instead of trying to remember dates, symptoms, pain levels, or repeated patterns from memory, users can prepare a structured summary from their logged data.
This can be useful before a doctor visit, consultation, or personal health discussion.
The report workflow is designed to summarize user-entered information, not to diagnose or replace professional evaluation.
Privacy Controls
Privacy was one of the main design priorities.
Rhythmiva includes privacy-focused features such as local-first tracking, optional cloud sync, app lock, anonymous local mode, AI consent controls, export options, local data deletion, and cloud account deletion.
The app allows the user to decide:
- What to track
- Whether to use the app locally or with cloud sync
- Whether to enable AI analysis
- Whether to attach photos
- Whether to export data
- Whether to create sharing links
- Whether to delete local or cloud data
This level of control is important because the app handles personal and sensitive information.
Attachments and Photo Questions
Rhythmiva supports attachments and photos for personal records.
Users can attach selected photos to their private logs or use photo-based questions with the AI assistant when they choose to do so. This can be useful when the user wants to keep visual records related to their own notes or questions.
The feature was designed as optional and user-controlled. Photos are not required for the core tracking workflow.
Sharing Links
Rhythmiva includes revocable sharing links for selected reports or AI results.
This feature was designed for cases where a user wants to share only a specific piece of information, rather than exposing the entire account or all tracking data.
The sharing concept is intentionally selective: the user chooses what to share and can revoke access when needed.
Reminders and App Lock
The Android version includes notification permission support and reminder scheduling, while the iOS version includes privacy-focused permission usage for Face ID and photo access.
The app lock feature helps protect private cycle data on the device. This is especially important for an app that may contain personal notes, symptoms, photos, and AI questions.
Reminder functionality supports regular use by helping users remember to log data or prepare for expected dates.
Technical Implementation
Rhythmiva combines several technical systems:
- Native iOS app built with SwiftUI
- Native Android app built with Kotlin and Jetpack Compose
- Local data model for period entries, daily logs, attachments, AI history, settings, and token balance
- Manual JSON mapping and tolerant sync decoding
- Local file-based storage
- Cloud API integration
- Cross-device sync logic
- Date normalization and calendar-day handling
- Biometric app lock
- Notification/reminder workflow
- AI assistant history
- Photo attachment support
- Report generation
- Export tools
- Account deletion workflow
- Privacy-focused UI and onboarding
One of the main engineering challenges was keeping iOS, Android, and cloud data compatible. The sync system needed to handle real-world data differences such as date formats, deleted items, numeric-keyed backend objects, duplicate notes, and AI history deletion across devices.
Another important part was designing the app so that local data and cloud data remain understandable to the user. Deleting local data and deleting a cloud account are different actions, and the app makes that distinction clear.
Medical and Privacy Positioning
Rhythmiva is designed for education, personal tracking, and appointment preparation only.
It is not a medical device, diagnostic service, contraception method, fertility treatment, pregnancy confirmation tool, or replacement for professional medical care. Cycle predictions and AI answers can be inaccurate or incomplete.
This positioning was important from both a product and compliance perspective. The app helps users organize and understand their own records, but it does not make medical decisions for them.
Result
Rhythmiva became a complete cross-platform private tracking product published for iOS and Android.
The project combines mobile development, privacy-aware product design, local-first data storage, cloud sync, AI workflow, appointment summaries, biometric protection, reminders, attachments, sharing, account deletion, and cross-platform consistency.
This project demonstrates my experience in iOS development, Android development, SwiftUI, Kotlin, Jetpack Compose, privacy-focused architecture, cloud API integration, health-related app design, AI feature integration, local data modeling, and building complete mobile products from idea to publication.
View on App Store: https://apps.apple.com/en/app/rhythmiva/id6773687000
View on Google Play: https://play.google.com/store/apps/details?id=com.kolesnyk.rhythmiva&hl=en