I built a privacy-first CBT journaling app as a solo founder

Hey everyone 👋

I’m a solo founder and I recently launched Cognitive Diary, a privacy-first self-reflection app that combines structured CBT journaling with guided breathing exercises.

I built it because I could not find a mental health app that felt both structured and truly private.

Most apps I tried had at least one of these problems:
• too much data collection
• heavy gamification
• no real cognitive structure

I did not want a social feed.
I did not want streak pressure.
I did not want user data as the business model.

I wanted a calm space where reflection feels intentional.

So I built Cognitive Diary around two core ideas:

1. Structured thinking inspired by CBT
   Instead of blank notes, users get guided formats like Automatic Thought Records, ABCDE belief reframing, anxiety monitoring, exposure logs with SUDS levels, mood tracking, and emotion regulation logs.

The goal is clarity, not engagement metrics.

1. Privacy by default
   All sensitive data is encrypted locally using AES-GCM and stored in a local SQLite database. The encryption key is generated on device and never sent to the backend.

Cloud sync is optional and only uploads encrypted blobs. The server cannot read journal content. Most features work fully offline and no account is required unless sync is enabled.

Tech stack

React Native
Expo
Firebase for auth and sync
RevenueCat for subscriptions

Bootstrapped. No VC. Solo founder.

Early lessons

Offline-first sync logic was harder than building the UI.
Positioning in mental health requires careful wording to avoid medical claims.
Privacy is valued, but it is surprisingly hard to communicate clearly.

I would really appreciate feedback from this community:

• Is privacy a strong enough differentiator for a B2C app?
• Does structured CBT journaling resonate, or is it too niche?
• If you have built in wellness or B2C SaaS, what traction channels worked for you?

Happy to answer any product or technical questions.