Short answer
Test the website on an actual phone. Check whether the navigation is obvious, text is readable without zooming, interactive controls are easy to tap, forms are reasonable, layouts stay stable, pages load efficiently, and the primary contact or purchase action is easy to reach.
Responsive design is a layout behavior, not a usability certificate.
Responsive CSS can rearrange columns, resize images, and change navigation at smaller widths. That is necessary. It does not automatically make the result pleasant to use.
A mobile site can still have tiny controls, excessive scrolling, intrusive overlays, unreadable text, long forms, unstable content, or a call to action that disappears below everything else.
Navigation should require less thinking, not more precision.
A phone screen has less room and touch is less precise than a mouse pointer. Menus should expose the important destinations without forcing the visitor through a maze of nested items.
Watch for:
- menu buttons that are visually hard to identify
- links packed too closely together
- important pages hidden behind multiple levels
- sticky elements covering the content
- menus that do not close or return focus correctly
Readable type matters more than fitting everything above the fold.
Do not shrink body copy simply to preserve a desktop composition. The visitor should be able to scan headings and read normal text at a comfortable size without pinch-zooming.
Line length, line height, contrast, spacing, and hierarchy matter as much as the nominal font size.
Tap targets should behave like things meant for fingers.
Buttons, menu items, form controls, close icons, and linked cards need enough size and separation that people can use them reliably. Accessibility guidance for mobile experiences specifically accounts for touch input and small screens, not only visual responsiveness.
Forms are a common place to lose a mobile visitor.
Ask only for information the business genuinely needs at that stage. Use proper input types so phones can show a useful keyboard. Keep labels clear. Do not force someone to type a long life story before they can ask a basic question.
W3C's form guidance notes that simpler forms are easier to understand and that unnecessary requirements increase the chance users abandon them.
Stability and speed affect the experience even when the design looks good.
Large images, autoplay media, heavy third-party scripts, poorly sized assets, and delayed fonts can make a page feel slow. Layout shifts can move the button someone was about to tap. A mobile review should include what happens while the page is loading, not only the screenshot after everything settles.
Make the next step easy to reach.
If the business wants calls, quote requests, bookings, directions, purchases, or project inquiries, the mobile layout should make that action obvious without turning the page into a permanent popup.
STATICMETHOD's Website Score includes mobile readiness and contact-path checks because those problems often reveal themselves before a full redesign is necessary.
Sources & further reading