The fix, in one snippet
<meta name="viewport" content="width=device-width, initial-scale=1">Illustrative values. Change the paths, hostnames and options to match your own site before using it.
The sections below explain what is tested, why it matters and the alternatives.
What we test
We read <meta name="viewport"> from every page and report those without one. The tag's presence is what is checked; its exact value varies legitimately between designs, and a layout may have good reasons for a particular initial scale.
The check reads the served HTML, so a viewport injected by JavaScript after load does not count. Neither does a crawler: by the time the script runs, the layout decision has already been made.
Why it matters
Google has indexed the mobile version of pages for every site since 2024. If the mobile rendering is a shrunken desktop layout, that is the version being assessed: the text is unreadable without zooming, tap targets overlap, and the page fails the usability checks that feed into ranking.
Without the tag, a mobile browser assumes a virtual viewport around 980 pixels wide and scales the result down to fit the screen. Every responsive breakpoint in your CSS is then evaluated against 980 pixels, so the mobile layout you wrote never activates.
This is a single-line fault with a total effect, and it is invisible on the desktop where most people test.
How to fix it
Add the standard tag to the head of every page, ideally in the base template so it cannot be missed:
<meta name="viewport" content="width=device-width, initial-scale=1">Do not add user-scalable=no or a maximum-scale below 5: preventing zoom is a WCAG failure under 1.4.4 and makes the page unusable for anyone who needs to magnify text.
Verify on a real narrow viewport rather than by resizing a desktop window, which does not reproduce the virtual viewport behaviour.
Where this fits
Viewport meta tag missing is check 1 of 7 that the seo & site health audit runs under technical seo and speed, ordered the way they are worth fixing. That ordering is the point: Fixing this one while the check above it still fails buys less than it looks like.
What fixing this still leaves open
Viewport meta tag missing closes one route in. Immediately below it: HTML served uncompressed, where hTML served without gzip or brotli transfers several times more bytes than it needs to; Render-blocking scripts in the head, where synchronous scripts in the head stop the parser; Slow server response, where how long the server took to return each page.
Found in the same scan
The seo & site health audit reports this alongside checks from other categories that are at least as serious, including Broken internal links, where an internal link that returns an error is a dead end for the reader and a wasted request for the crawler, and Crawl errors (4xx / 5xx), where uRLs reached during the crawl that returned a client or server error. A single run of seo & site health audit answers all of them at once.
The first few lines
You are a senior web engineer. I ran a security and SEO scanner against my site and it reported the finding below. Fix it properly rather than suppressing the symptom.
Finding: Viewport meta tag missing (high severity)
Scanner check id: seo-viewportThe rest of this prompt names the pages and line numbers we found the problem on, the configuration to change, and the constraints a good answer has to respect. It is free, it just needs an account so the work is not scraped wholesale.
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