Our mobile UI rules

We build mobile apps for clients, and we build one for ourselves — a Hyrox coaching app that we use in our own training, every day. That second part matters. When you are the user, mid-workout, heart rate at 170, every design mistake punches you in the face within a week.

These are the rules that survived. We apply them to everything we ship.

1. One thumb, ten seconds

The realistic mobile moment is not a person on a sofa giving you their full attention. It's someone between sets, gloves half off, with ten seconds and one available thumb. Every core action has to survive that moment: reachable with one thumb, done in one or two taps. If a feature lives three taps deep, it doesn't really exist.

2. Dark by default

Our app is dark because its environment is dark-ish and glare is real: gym lighting, 6 a.m. sessions, sweat on the screen. Dark backgrounds make the content — numbers, photos, charts — do the talking, and high-contrast accents (ours is orange in the app) read instantly. If your users check your app in bed, at dawn, or under fluorescent light, dark isn't an aesthetic choice. It's ergonomics.

3. The number is the interface

On our summary screen, the calorie count is set in huge dot-matrix digits you can read at arm's length on a treadmill. That's deliberate: the biggest thing on any screen should be the thing the user came for. Not your logo, not a card carousel — the number. Everything else steps back. When you can't decide what to enlarge, you haven't decided what the screen is for.

4. Five tabs, no more

Home, Workout, Coach, Meal, Progress. That's the whole app. A bottom bar with five tabs is the entire navigation budget — the moment a feature can't find a home in one of five, we question the feature, not the nav. "More" menus are where features go to die.

5. Streaks must be honest

Our streak counter can be lost. That's the point. A streak that forgives everything is a decoration, and users can smell it. Honest streaks respect the user enough to tell the truth — which is also why they work. Motivation mechanics are fine; dark patterns that manufacture fake progress are not.

6. Never ask what you can measure

If the camera can count reps, don't make an athlete type a number with sweaty hands. Every manual input field is a place where users quit. The order of preference is: sense it, infer it, then — only when there's no other way — ask for it.

7. Ship it to yourself first

Every rule above was found the same way: we shipped something, used it in training, and it either survived or it didn't. No focus group finds these things. If you can't be your own user, get your product into real hands early enough that reality can still change the design.

None of this is specific to fitness. Swap the gym for a clinic waiting room, a shop counter, a delivery van — the moment is the same: one thumb, ten seconds, poor lighting, a user who is doing something else. Design for that person and the sofa user gets a great app for free.

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Building something like this? hello@tonric.com