Test on a real device

Get your deployed URL onto a real phone. If you have an Android device, connect it by USB and open chrome://inspect on your laptop for full DevTools against the page. On iOS, connect it and use Safari’s Develop menu. Both take about five minutes to set up the first time and are useful to know permanently.

Then turn off wifi on the phone. Use the mobile network. This is the single most informative thing in this chapter, your site on a real connection rather than a throttled simulation of one.

Now use it one-handed, the way you use your own phone. Do the main task your site is for. Do not be gentle with it.

Write down everything. A target you missed. Text you had to zoom to read. A form field hidden by the keyboard. Something that took longer than you expected. A tap that did nothing visible so you tapped again. An animation that stuttered. Somewhere you had to change your grip.

Run Lighthouse in mobile mode against the deployed URL and record the numbers, but treat them as a second opinion rather than the verdict, it is a simulation, and your list from the previous step is primary evidence.

Fix the top three. Then go back to the phone, on mobile data, and do the task again. Note whether it feels different. That before-and-after sentence is what goes in your write-up, and it is worth more than the Lighthouse score.