How I built an Apple Watch workout app using Cursor and XCode (with zero mobile app experience) | Terry Lin

09/15/25
Source: Lenny’s Newsletter by Claire Vo. Read the original article

TL;DR Summary of How Terry Lin Built an AI-Powered Voice Fitness Tracker Across iPhone and Apple Watch

Terry Lin developed a voice-powered fitness tracking app that simplifies workout logging across iPhone and Apple Watch. He leverages a dual workflow using Cursor and Xcode to enhance coding and debugging efficiency. His innovative AI collaboration methods, including a three-step create-review-execute process and vibe refactoring, optimize both code quality and productivity. The app also uses GPT-4 and index cards for rapid prototyping and improved interface design.

Optimixed’s Overview: Innovating Fitness Tracking with AI-Driven Voice Integration and Developer Workflows

Introduction to the AI-Powered Fitness App

Terry Lin, a product manager and developer, created Cooper’s Corner, an AI-enabled fitness app designed to eliminate tedious manual workout logging. By simply speaking exercises, weights, and reps, users can track their progress seamlessly on both iPhone and Apple Watch.

Key Features and Development Workflow

  • Voice-Activated Tracking: Intuitive voice commands allow effortless workout input, enhancing user experience.
  • Cross-Device Compatibility: Synchronizes data across Apple devices for consistent fitness monitoring.
  • Analytics and Progress Visualization: Built-in analytics track workout consistency and improvements over time.

Dual-Wielding Development Tools for Enhanced Productivity

Terry employs a dual-wielding workflow by using Cursor for coding and Xcode for building and debugging the app. This combination streamlines development and debugging processes, allowing for rapid iteration and fixes.

Optimizing AI Collaboration in Coding

  • Three-Step AI Workflow: Create, review, and execute—this approach ensures reliable and refined code generation with AI assistance.
  • Vibe Refactoring: A technique to keep code well-organized and readable for both humans and AI, improving maintainability and performance.
  • Token Conservation: Methods to optimize file size and AI prompt efficiency for better performance and reduced computational load.
  • Rubber Duck Technique: Using AI-generated code explanations to deepen understanding and accelerate learning.

Rapid Prototyping and Interface Design

Terry incorporates index cards and GPT-4 to quickly prototype mobile interfaces, enabling agile design iterations and creative exploration. This fusion of human creativity and AI assistance drives effective app development and user experience enhancements.

Conclusion

By integrating AI-powered voice tracking with advanced developer workflows and AI collaboration techniques, Terry Lin’s Cooper’s Corner app sets a new standard for fitness tracking apps. It showcases how thoughtful AI usage can revolutionize both product development and user engagement.