Common Mobile UX Mistakes and How to Avoid Them

The most expensive assumption about mobile design is that it's the narrow version of the desktop design.

That assumption is rarely stated out loud. It shows up in the process instead: the design gets made on a wide screen, someone says "let's check mobile" near the end, and the layout is squeezed. What comes out is technically responsive. It wasn't designed for mobile.

What follows are the mistakes we run into most often, and why most of them go unnoticed until launch.

Narrowing isn't prioritising

Three columns sitting side by side on desktop stack on mobile. Technically nothing is wrong. But the meaning of the page has quietly changed.

Three things that were visible at once are now in an order. The primary action living in the right-hand column — immediately visible on desktop — can end up two screens down on a phone. Nobody made that decision. The layout made it.

This is where the real work of mobile design starts: deciding what comes first. When that decision isn't made, source order makes it for you.

Content priority is also an opportunity to cut. If a section isn't genuinely needed on mobile, the question might not be "where do we put it?" but "is it needed on desktop either?"

Touch targets are smaller than they look

A mouse can hit a single pixel. A finger can't.

Small touch targets are usually a side effect of a visual preference: a fine icon, a compact list, a tight menu. It looks elegant on screen and gets missed in the hand.

WCAG 2.2 defines a minimum target size, and platform guidelines generally suggest something more comfortable. But the thing that matters before any number is this: the touchable area can be larger than the visible one. An icon can be drawn small and, with the padding around it, still be a comfortable target. Growing the target without growing the design is usually possible.

How close targets sit to each other is a separate problem. Two small buttons side by side are riskier than one small button alone — hitting the wrong thing is worse than hitting nothing.

Layers that eat the screen

Vertical space is scarce on a phone. A fixed header, a fixed cookie bar, and a promotional strip all at once leave very little room for the thing people came for.

Each of those layers looks reasonable on its own. The problem is the sum, and usually nobody sees the sum, because each was added at a different time.

Layers with a small or unreachable close button are much worse on mobile, too. A small cross in the corner is fine on a desktop; a cross a thumb can't reach on a phone is the fastest way to make someone leave.

What happens when the keyboard opens

Forms behave differently on mobile, and that behaviour usually goes untested.

When the keyboard opens, the visible area shrinks. The field being filled can end up underneath it; the submit button can disappear; a fixed header narrows what's left even further. People end up typing without seeing what they're typing.

The keyboard type is a design decision too. A letter keyboard on an email field, a full keyboard on a phone number field — small details, but each wrong keyboard hands the user extra work.

The honest way to test a form on mobile is to actually fill it in, not to look at it.

Horizontal overflow

Sideways scrolling on mobile is almost always an accident. The page drifts a little to one side, the layout looks broken, and nobody can tell why.

The cause is usually small: a fixed-width element, a long word that won't break, a decorative image placed off-canvas, a negative margin. Being small is exactly why it survives to production.

The trap here is that overflow-x: hidden covers it easily. That doesn't remove the cause — it hides the symptom, and sometimes introduces new scrolling problems of its own. Finding the offending element takes longer and actually fixes it.

Weight hurts more on mobile

The same page is a very different experience on a mobile connection and a weaker device.

A large image that goes unnoticed on desktop produces a visible wait on a phone. An animation that runs smoothly on a good machine can stutter on a low-powered one. If a decorative transition delays someone reaching their goal, it costs more on mobile.

None of which means motion is banned on mobile. It means the budget is tighter.

Nothing replaces a real device

Device emulation in browser dev tools is useful and limited. It imitates screen size. It doesn't imitate a finger, a keyboard, a connection, a processor, or a screen in sunlight.

A few minutes on a real phone teaches more than hours of guessing — particularly about three things: are the targets big enough, can the form be filled in, does the page actually feel fast.

We prefer to handle these conditions at the design stage in our web work. A mobile version repaired at the end usually costs more.

Before you ship mobile

Most mobile mistakes don't come from missing knowledge. They come from ordering: when mobile is handled last, all that's left to do is make things fit.

Reversing that order makes the work easier. Decide what's genuinely necessary on the narrow screen first, and the wide screen becomes an expansion rather than a reduction.