Sthenos
AI-driven calisthenics coach: weekly generated sessions, a roadmap of skills to unlock and progress tracking.
- Year
- 2026
- Role
- Product design, architecture & development (solo)
- Stack
- Next.jsTypeScriptTailwind CSSCloudflare WorkersD1 / DrizzleBetter AuthAPI Anthropic
Context
Beginners and stuck practitioners give up for lack of a suitable program and a structure that survives missed weeks. Sthenos acts as a virtual coach: the user declares their maxes and how sessions felt, the AI (Anthropic API) generates and adjusts their sessions week after week, with a gamified skill roadmap and progress charts. The product priority is retention, not raw performance.
What I built
- Designed an AI coach whose business logic lives in the system prompt and the context injected from the database — the application only stores, transmits and displays.
- Structured input/output contract (JSON) between the app and the Anthropic API: profile, performance and feedback logs in; a detailed, progressive and justified session out.
- Progression model combining a skill roadmap (a tree of 7 families × 5 tiers, unlocked by prerequisites) and a per-exercise Skills view.
Screens
