Guides
Responsive testing guides
Short, practical answers to the questions developers ask when a layout has to work on a phone: what width the page really gets, how to reach your dev server, and how to see what’s going on.
iPhone Duo viewport size: what Safari gives your page
382, 594, 669 or 951 CSS pixels wide, depending on the pose. The full table, what breaks, and how to test each width.
How to open localhost on your iPhone
Why localhost doesn’t work on the phone, the one flag most dev servers need, and how to reach your Mac from anywhere with Tailscale.
How to inspect element on iPhone
Safari Web Inspector with a Mac, the options on Windows and Linux, and what you can still do with only the phone.