Without a viewport meta tag, a phone renders the page as if it were about 980 pixels wide and then shrinks it to fit the screen. Everything looks tiny, and your responsive CSS never applies. This one line in the <head> fixes it:
<meta name="viewport" content="width=device-width, initial-scale=1">
width=device-width tells the browser to use the phone's real width in CSS pixels; initial-scale=1 starts the page at normal zoom.
Mistakes to avoid
Disabling zoom. Values such as maximum-scale=1 or user-scalable=no stop people from zooming in. People with low vision rely on pinch-zoom, and accessibility guidelines treat blocking it as a failure. Most mobile browsers now ignore it partly, but not all do. Of the 24 sites SignalCrawler audited in September and October 2026, 5 disabled pinch-zoom.
Some sites add it to stop iPhones from zooming into form fields. The proper fix is to set form fields to at least 16 px font size; Safari then does not zoom.
A fixed width. width=1024 or another number makes the page that wide on every phone, which is the same as having no responsive design.
Two viewport tags. A theme and a plugin both adding one. The browser uses one of them, and you may not like which.
Setting it with JavaScript after load. The page first renders at desktop width and then jumps. Put the tag in the HTML.
How to check it
- View the page source and search for
name="viewport". There should be exactly one. - In Chrome's device mode at 375 px, text should be readable without zooming.
- Try pinch-zoom on a real phone: it should work.
Frameworks
Most frameworks add the tag for you. In Next.js the App Router adds it by default and you change it with the viewport export; in WordPress the theme adds it in header.php or through wp_head. If a page looks shrunk on phones, check that the template you use for it really outputs the tag.
What SignalCrawler checks here
The audit reports pages without a viewport tag and pages that disable pinch-zoom, then measures the layout at ten widths from 320 pixels up: horizontal scroll, small text and tap targets, and form fields small enough to make iPhones zoom.