Solo Developer Builds Three-Tier AI Fallback System for Fitness Roast App

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A solo developer has launched LOCK TF IN, an iOS fitness accountability app that uses an AI coach to mock users who skip workouts. The app's core feature relies on a three-tier fallback system: on-device Apple AI models for supported devices, a Cloudflare Worker proxying cloud AI for free users on older hardware, and a library of hand-written roasts as a last resort. Because the AI-generated roast is the app's entire value proposition, a failed AI response would render the product non-functional, making reliability engineering critical. The developer noted that crafting convincing fallback copy was unexpectedly time-consuming, as a poor fallback risks breaking the satirical tone the app depends on. Built solo using SwiftUI, LOCK TF IN is now available on the App Store.

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