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How I built an Apple Watch workout app using Cursor and Xcode (with zero mobile-app experience)

Terry Lin is a product manager and developer who built Cooper’s Corner, an AI-powered fitness tracking app that works across iPhone and Apple Watch. Frustrated with traditional fitness apps that require extensive setup and manual logging, Terry created a solution that lets users simply speak their exercises, weights, and reps. The app automatically structures this data and provides analytics on workout consistency and progress. In this episode, Terry shares his vibe-coding process using Cursor and Xcode and explains how he optimizes his codebase for AI collaboration. *What you’ll learn:* 1. How Terry built a voice-powered fitness tracker that works across iPhone and Apple Watch 2. His “dual-wielding” workflow, using Cursor for coding and Xcode for building and debugging 3. Terry’s three-step process for working with AI: create, review, and execute 4. Why optimizing your codebase for AI collaboration can dramatically improve productivity 5. How to use index cards and GPT-4 to rapidly prototype mobile interfaces 6. A technique for “vibe refactoring” that keeps code organized and optimized for both human and AI readability 7. His “rubber duck” technique to better understand generated code and improve your learning process *Brought to you by:* Paragon—Ship every SaaS integration your customers want: https://useparagon.com/HowIAI Miro—A collaborative visual platform where your best work comes to life: http://miro.com/ *Where to find Terry Lin:* LinkedIn: https://www.linkedin.com/in/itsmeterrylin/ GitHub: https://github.com/itsmeterrylin *Where to find Claire Vo:* ChatPRD: https://www.chatprd.ai/ Website: https://clairevo.com/ LinkedIn: https://www.linkedin.com/in/clairevo/ X: https://x.com/clairevo *In this episode, we cover:* (00:00) Introduction to Terry and his fitness tracker app (02:30) Demo of the voice-powered workout tracking across devices (06:40) Analytics and history views for tracking consistency (07:20) Dual-wielding Cursor and Xcode for mobile development (09:05) Building a v1 using AI tools (11:19) A three-step AI workflow: create, review, execute (19:38) Token conservation and vibe refactoring explained (23:25) Optimizing file sizes for better AI performance (25:28) Using “rubber duck” rules to learn from AI-generated code (28:13) Prototyping with index cards and GPT-4 (31:20) Human creativity and the last 10% (32:29) Lightning round and final thoughts *Tools referenced:* • Cursor: https://cursor.sh/ • Xcode: https://developer.apple.com/xcode/ • GPT-4: https://openai.com/gpt-4 • UX Pilot: https://uxpilot.ai/ • Figma: https://www.figma.com/ • Linear: https://linear.app/ *Other references:* • Apple UI Kit: https://developer.apple.com/design/human-interface-guidelines/ _Production and marketing by https://penname.co/._ _For inquiries about sponsoring the podcast, email jordan@penname.co._

Claire VohostTerry Linguest
Sep 15, 202536mWatch on YouTube ↗

CHAPTERS

  1. 0:00 – 1:11

    Why a voice-first workout tracker: from gym inconsistency to structured analytics

    Claire and Terry set up the core problem: staying consistent at the gym is hard, and traditional fitness apps feel like too much setup and manual logging. Terry explains the spark—using the ChatGPT mobile app as speech-to-text—and the idea of turning voice into structured workout data with analytics.

    • Pain point: forgetting routines after gaps in training
    • Existing apps require heavy setup, accounts, and manual input
    • Insight: speech-to-text can capture workouts hands-free
    • Goal: turn voice into structured records + analytics
  2. 1:11 – 2:38

    Sponsor: Paragon (product integrations)

    Claire shares a sponsor message about Paragon, a tool for shipping product integrations faster than building in-house or relying on limited unified APIs. The pitch emphasizes high-volume ingestion, real-time actions, and reducing integration build time from months to days.

    • Integrations as a critical product/SaaS requirement
    • Limitations of embedded iPaaS and unified APIs
    • Paragon’s focus on fast, reliable integrations
    • Call to action and discount link
  3. 2:38 – 4:23

    What Terry built: Cooper’s Corner across iPhone + Apple Watch

    Terry introduces Cooper’s Corner, a mobile fitness tracker built with AI, and describes the desired experience: minimal friction, no “homework,” and fast logging. Claire frames the episode as a mobile/watch-focused AI-building walkthrough using Cursor, Xcode, and even index cards.

    • App concept: voice-powered workout tracking
    • Cross-device experience (iPhone + Apple Watch)
    • Positioning: reduce friction vs traditional trackers
    • Tools: Cursor + Xcode; prototyping with index cards
  4. 4:23 – 6:42

    Live demo: voice logging, transcription, and sync between Watch and phone

    Terry demos Sign in with Apple and the core flow: speak an exercise, weight, and reps, then see it transcribed and saved as a structured log. The same workflow works on both Apple Watch and iPhone, with data syncing between devices for in-gym convenience.

    • Authentication choice: Sign in with Apple for low-friction onboarding
    • Voice capture on Watch and phone
    • Automatic transcript + structured fields (exercise/weight/reps/time)
    • Cross-device sync so either device can log workouts
  5. 6:42 – 7:23

    Analytics and history views: consistency tracking and progression over time

    Terry shows the app’s history and analytics features that help answer “have I been consistent?” and “am I progressing?” Users can view 7/30/90-day activity, top exercises, and per-exercise history including a visual progression view.

    • Consistency metrics (e.g., gym days in last 30 days)
    • Top exercises surfaced from logs
    • Per-exercise drill-down with historical records
    • Progress visualization (e.g., scatter plot of weight over time)
  6. 7:23 – 9:22

    Dual-wielding Cursor and Xcode: a practical mobile AI dev setup

    Terry explains why iOS development typically requires Xcode, and how he pairs it with Cursor by pointing both tools at the same project folder. Cursor handles most code generation/edits, while Xcode remains essential for builds, simulator/device runs, and debugging compile-time issues.

    • Xcode as required Apple IDE for building iOS/watchOS apps
    • Side-by-side workflow: Cursor codes, Xcode builds/debugs
    • Mobile debugging differs from web (no simple localhost + console loop)
    • Watch builds/testing add extra complexity
  7. 9:22 – 11:28

    From zero to v1: Voice Memos → Python → GPT → spreadsheet, then a real backend

    Terry walks through his earliest prototype: recording workouts via Apple Voice Memo on the Watch, moving files to a computer, and using a Python script + GPT-4 to generate a spreadsheet. The limitations of unstructured spreadsheet outputs pushed him toward a database and backend API for consistent, queryable data.

    • MVP: record voice notes, then transcribe and summarize via GPT
    • Python automation to output results into Excel
    • Problem: inconsistent/unstructured data limits analytics
    • Next step: database + backend API for structured data (foreign keys, consistency)
  8. 11:28 – 13:14

    Three-step AI workflow in Cursor: PRD create → PRD review → PRD execute

    Terry outlines a repeatable system for getting reliable results from AI coding: generate a PRD, have a model critique it for gaps, then execute via a phased checklist. He uses Gherkin-style scenarios, explicit file lists, and pause points with Git commits to reduce risk and improve one-shot success rates.

    • PRD creation rule to turn an issue into an implementation plan
    • PRD review rule: rate “could another model execute this with zero context?”
    • Execution rule: phased checklist with stop points
    • Use of Gherkin user stories and explicit file/endpoint references
    • Safety: Git commits before/after phases to enable rollback
  9. 13:14 – 19:47

    Sponsor: Miro (Innovation Workspace)

    Claire shares a sponsor message about Miro’s Innovation Workspace and its AI copilot to turn brainstorm artifacts into diagrams, product briefs, and prototypes. The segment emphasizes faster iteration, collaboration, and reducing cycle time.

    • AI copilot inside a collaborative canvas
    • Turn stickies/screenshots into structured outputs
    • Supports roadmaps, briefs, diagrams, and prototyping
    • Call to action to visit Miro
  10. 19:47 – 23:26

    Token conservation and “vibe refactoring”: keeping AI output manageable

    Claire and Terry dig into why limiting tokens and context can improve outcomes: large files and verbose generations slow the workflow and increase errors. Terry describes “vibe refactoring” as a planned phase where AI helps reorganize and clean code after rapid feature-building to reduce tech debt and improve reliability.

    • Motivation: sanity/performance, not just cost
    • Large files increase context churn and model mistakes
    • AI can generate working code fast but may introduce tech debt
    • Dedicated refactor workflow/rule with QA checkpoints
  11. 23:26 – 25:29

    Optimizing for your AI teammate: smaller files, line counts, and easier navigation

    Terry explains a concrete codebase design principle: keep files small enough that the model can reason over them efficiently. He uses quick line-count scans to identify “god files” and breaks them down, aiming for ~200–400 lines so the AI spends fewer tokens reading irrelevant context and makes fewer mistakes.

    • Design principle: file size optimized for LLM context handling
    • Technique: line-count to find refactor targets
    • Example: ~900-line recorder file flagged for refactor
    • Phased refactor plan with compile/error checks and safety checklist
  12. 25:29 – 29:01

    “Rubber duck” rule: using AI to explain, quiz, and accelerate learning

    To avoid shipping code he doesn’t understand, Terry uses a “rubber duck” workflow where the model explains files line-by-line and even quizzes him. This turns AI-assisted building into a learning loop, improving debugging instincts and helping him spot model mistakes faster over time.

    • Rubber-ducking: explain code as a learning/debugging tool
    • Model-generated walkthroughs and “pop quiz” prompts
    • Addresses fear: vibe coders shipping code they don’t understand
    • Improves long-term speed by building debugging intuition
  13. 29:01 – 31:22

    Design exploration on the subway: index-card prototypes → GPT-4 upscaling → Figma UI kit

    Terry shows his low-tech-to-high-tech design pipeline: sketch screens on index cards when offline, photograph them, then use GPT-4 image capabilities to “upscale” into clearer mockups. He then moves designs into tools like UXPilot/Figma and uses Apple UI libraries to quickly assemble realistic iOS layouts.

    • Offline prototyping with index cards (mobile aspect ratio)
    • Upload sketches to GPT-4 to generate higher-fidelity variations
    • Transfer into Figma via tooling (e.g., UXPilot)
    • Leverage Apple UI kit/components for fast, native-feeling designs
  14. 31:22 – 32:28

    Human creativity and the last 10%: where AI still struggles (especially in design)

    Claire and Terry reflect on the gap between “80% good” AI outputs and the craft required to polish the final experience. They argue the differentiator is often the last 10%—interaction details, visual refinement, and product judgment—and side projects help PMs empathize with engineering/design tradeoffs.

    • LLMs often get you to 80% quickly; final polish is hardest
    • Design refinement and craft remain a key human advantage
    • Pragmatism: ship MVP, then iterate where it matters
    • Side projects improve PM communication with engineers/designers
  15. 32:28 – 35:21

    Lightning round: mobile debugging asks, model quality, and Git-based risk control

    Terry shares practical wishes for mobile AI tooling (better visibility into on-device behavior like network traffic), and comments on LLM code quality for mobile ecosystems. He also explains his main control mechanism: frequent Git commits to mitigate risk when the model drifts off track.

    • Tooling ask: better mobile observability (e.g., network inspection)
    • LLM quality: generally good; occasional issues with outdated patterns
    • Strategy when models drift: frequent Git commits and rollbacks
    • A disciplined, incremental approach vs “YOLO” large commits
  16. 35:21 – 36:16

    Where to find Terry + closing wrap

    Claire closes the episode with thanks and a call for viewers to like/subscribe and leave reviews. Terry shares where people can connect with him online.

    • Contact: Terry on LinkedIn and X
    • Episode wrap and audience calls-to-action
    • Podcast availability across platforms

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