What the meta tag analyzer reports
Paste a page's source and this meta tag analyzer reads the head: the title and its length, the meta
description and its length, charset, viewport, the robots directives, the canonical link, the
Open Graph and Twitter card tags, the lang on the <html> element, every declared hreflang,
and any tag that appears more than once.
Each finding is graded. An absent canonical is a note; a title over the truncation point is a warning; a missing charset, a duplicated tag or a noindex directive is an error, because each of those changes what happens to the page rather than how it looks.
Analysing is not generating
If what you need is the markup itself, the Meta Tag Generator writes it for you with a SERP preview beside the fields. This page answers the opposite question: something is already live, and you want to know what is really in its head. The two intentions rarely arrive at the same moment, which is why they are two pages.
Why paste, and where to get the source
A script in your browser cannot read another origin's HTML — the security model forbids it, and the sites you want to inspect do not opt out. The alternative on offer elsewhere is a server that fetches your URL on your behalf and keeps a record of it. Copying the source sidesteps that, and it is the only method that works on a page behind a login or on a build that has not shipped.
Take the source with Ctrl+U, or copy the head from DevTools if a tag manager injects anything.
Paste the whole document if you like; everything outside the head is ignored, and markup inside
comments or <script> blocks is skipped so a templated example does not register as a real tag.
The tags that change behaviour
charset decides how bytes become characters. Without it the browser guesses, and a wrong guess is where mojibake comes from. It must be the first thing in the head, inside the first kilobyte.
viewport is what stops a phone rendering your page at desktop width and shrinking it. Since indexing is done with a mobile crawler, a page without it is being judged in the state it looks worst.
robots is the only tag here that can remove a page from search on its own. noindex withdraws
it; nofollow stops every link on it from passing anything, internal navigation included; none
does both. The analyzer treats any of them as an error precisely because the tag is invisible in
the rendered page.
canonical does not force anything. It tells Google which address you would prefer among several that serve the same content, and Google usually agrees. Two canonical links on one page, however, cancel each other out, which is why duplicates are reported.
The tags that only change the presentation
Title and description are not ranking factors, and it is worth saying plainly. What they control is the sentence a searcher reads before deciding whether to click, and Google reserves the right to rewrite either one. Descriptions are rewritten more often than titles because a query-specific snippet from the body is frequently more useful than a generic summary.
That is not an argument for skipping them. When your description is used, it is the only piece of sales copy in the result, and it costs a minute.
Open Graph does not touch search at all. It decides whether a link pasted into Slack, WhatsApp or LinkedIn expands into a card or stays a naked URL, and the difference in click-through is large enough that it belongs on every page you expect anyone to share.
Once the head is clean, the Heading Structure Checker does the same job for the body, and the Mixed Content Checker finds the assets still loading over plain HTTP.