Case study · mobile · 2026

ugoki: a coach in your pocket.

A native wellness app pairing intermittent fasting with short high-intensity workouts, coached by an AI that is governed like production software. Designed and built solo; a cold outreach brought investor interest from a London venture firm.

A live product of my own, built outside this concept. Not work for Fin, and not affiliated with them.

curated workouts: 23
exercises with video: 114
fasting protocols: 3
achievements in the habit loop: 21

The context

Busy professionals do not lack information about health; they lack twenty spare minutes and someone who notices when they quietly stop. UGOKI pairs intermittent fasting with short high-intensity training and wraps them in a coach that remembers you. Everything fits in fifteen to twenty minutes a day, the budget a working week offers.

The bet

The coach is the product: constitutional rules that put safety above engagement, skills that load by query, memory that carries goals and injuries across sessions, and an automated judge scoring every answer for drift.

The UGOKI workout library: search, HIIT and strength filters, featured workouts with duration and calorie load, and personalised recommendations — Three core surfaces: the workout library shows duration and calorie load before commitment; the fasting timer makes pause and extend first-class controls, because rigid tools get abandoned; and the coach wears its guardrails on screen. Tap a capture to open it full size.

The UGOKI fasting timer mid-fast: elapsed time, time remaining, and end, extend and pause as first-class controls — Three core surfaces: the workout library shows duration and calorie load before commitment; the fasting timer makes pause and extend first-class controls, because rigid tools get abandoned; and the coach wears its guardrails on screen. Tap a capture to open it full size.

The design decisions

The coach is governed, not just prompted.

Constitutional rules order safety over evidence and evidence over enthusiasm; skills for workouts, fasting, nutrition, motivation and research load by query; memory persists across sessions; and an LLM-as-judge loop scores every answer. The interesting design surface of an AI product is the rules, not the chat.

Guardrails live in the interface.

"For general wellness guidance only. Not medical advice." sits permanently on the coach screen, and suggested prompts keep the conversation inside the coach’s competence. The same rule as my transit platform: the AI advises, the human decides.

Native, on one token contract.

Expo and Tamagui with a tiered token system, the same primitives-beneath-a-semantic-contract structure I build on the web, so screens land consistent on iOS and Android without per-platform pixel pushing.

Empty states do the onboarding.

A tracker with no data yet has one job: make day one feel startable. The first-run dashboard leads with the next action (start a fast, log a weight, open the first workout) rather than presenting a wall of zeros as a verdict.

Health data arrives on its own.

Apple HealthKit and Google Health Connect sync metrics automatically, so the habit does not depend on manual logging.

Different users run on different fuel.

Streaks, XP and achievements for the momentum-driven; friends, leaderboards and challenges for the socially driven; blood-work upload with AI-parsed biomarkers and a PubMed-backed research hub for the evidence-driven. The habit loop is visible, whichever engine drives it.

Where it stands

Feature-complete across fasting, workouts, the coach, social and research, with a Cardano rewards wallet in progress. Expo SDK 52 and Tamagui on the front, FastAPI and PostgreSQL behind, deployed on Fly.io. A cold LinkedIn message put it in front of a London venture investor; the walkthrough is the full story.

What I learned

The hardest screen in a habit app is the one with nothing on it yet. And an AI coach earns trust the way a human one does: by remembering, and by staying inside its competence. Both are design problems solved outside the chat window.