Making AI Feel Human in a Mobile App with Expo, Reanimated, and Skia
Article Summary
Daehyeon Mun built an AI companion app that earned 4.9 stars and won Expo's Most Creative App award. As a solo mobile engineer, he used custom shaders and worklet-based animations to make AI feel emotionally intelligent.
Callie is a self-care app for eating disorder recovery that required extreme sensitivity in every interaction. Mun engineered the entire mobile experience using Expo, React Native Reanimated, and Skia shaders to create warm, calm visuals that feel human rather than mechanical. The app has over 3,200 App Store reviews averaging 4.9+ stars.
Key Takeaways
- Custom Skia shaders create page curl effects that make AI journals feel handwritten
- Worklet-based libraries run on UI thread, preventing frame drops in sensitive interactions
- Expo CNG and OTA updates enabled weekly feature releases without App Store delays
- Tone-shaping logic filters AI responses to stay gentle and non-judgmental
- Solo engineer shipped polished app by eliminating native config overhead
A one-person team built a 4.9-star AI health app by using Expo's infrastructure to focus engineering time on pixel-perfect emotional design instead of build configuration.
About This Article
Daehyeon Mun was building an app for eating disorder recovery and needed animations that could respond to what users were actually doing in real time. Tools like Lottie and Rive play back pre-made animations, so they couldn't capture the subtle emotional shifts that mattered for this use case.
Mun built custom shaders in React Native Skia using geometric transformations and trigonometric functions. This let him create visuals that actually deform based on how users interact with them. A page curl effect, for example, bends in response to touch instead of just playing a fixed animation.
The result felt different. Callie's AI journal feature reads like a handwritten letter instead of something a machine generated. The app was named Expo's Most Creative App of 2025 and has maintained a 4.9+ star rating across more than 3,200 reviews.
