Design for one hand and short, interrupted sessions. Keep main actions within thumb reach and tap targets at least 44 by 44 points. Use shallow, conventional navigation. Minimize typing. Design offline, loading and error states. Ask for permissions only when the feature needs them, and test on real phones.
Design for the hand
Put the actions people use most where a thumb reaches them, usually the lower part of the screen, and keep destructive actions away from them. Apple's design guidance says to "create controls that measure at least 44 points x 44 points so they can be accurately tapped with a finger." WCAG 2.2 sets a lower floor for accessibility conformance: success criterion 2.5.8, Level AA, requires pointer targets of at least 24 by 24 CSS pixels, with exceptions such as enough spacing.
Navigation
Users bring habits from every other app on their phone. Keep navigation:
- Shallow: the main sections one tap away, usually in a tab bar of a few items.
- Conventional: follow iOS and Android patterns for back, tabs and menus.
- Clear position: the user always knows where they are.
- Search where content is large.
Onboarding and permissions
Get users to the first useful result quickly; skip long tours. Ask for permissions such as location, camera or notifications at the moment a feature needs them, with a sentence on why, rather than all at launch. Let people explore before forcing an account where the app allows it.
Forms and input
Typing on a phone is slow and error-prone:
- Ask only what you need; use defaults and remember earlier answers.
- Use pickers, toggles and steppers instead of typing where possible.
- Show the right keyboard for each field: numbers, email, phone.
- Support autofill and password managers.
- Show errors beside the field as the user goes.
Offline, loading and errors
Mobile connections drop. Show cached content when offline, say clearly when something could not be saved, and retry quietly where safe. Show progress for anything that takes time, and write error messages that say what happened and what to do, in line with Nielsen's heuristic of helping users recognize, diagnose and recover from errors in his 10 usability heuristics.
Accessibility
Build accessibility into components from the start, measured against WCAG 2.2 Level AA:
- Support the system text size settings without breaking layouts.
- Label every control for screen readers.
- Meet contrast requirements, including in dark mode.
- Never rely on color or gestures alone; offer a visible alternative.
Testing on real phones
Test the main tasks on real devices, in the conditions people use them: one hand, outdoors, on a slow connection. Nielsen's article on testing with five users (2000) argues that small rounds of about five find most problems. Test on both iOS and Android if you ship both, since conventions differ.
Common mobile UX mistakes
The faults we see most often:
- Desktop layouts shrunk to fit. Design for the phone first.
- Tiny tap targets packed close together.
- Permission requests at launch before users see any value.
- Hidden navigation for main sections.
- No offline or error states. The app looks broken on a weak signal.
Conclusion
Mobile app UX design starts from one hand, a small screen and interrupted sessions. Keep main actions within thumb reach and tap targets at least 44 by 44 points as Apple advises, above WCAG 2.2's 24 by 24 CSS pixel minimum; keep navigation shallow and conventional; cut typing; design offline, loading and error states; ask for permissions in context; and test on real phones in small rounds.
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