AMP Page URL is missing the <html amp> tag
This means that the URL in question defines an AMP Page URL that does not contain an <html amp> tag.
Why is this important?
AMP HTML documents are required to contain a top-level <html amp> tag. If the tag is not present, search engines may not consider the HTML valid and may not index the page properly, or include it in search results.
What does the Hint check?
This Hint will trigger for any internal URL which references an AMP Page, which does not include the <html amp> tag.
Examples that trigger this Hint
Consider the URL: https://example.com/page-a/
The Hint would trigger for this URL if it included a <link> tag that referenced an AMP page:
where this AMP page had no <html amp> or <html ⚡> tag in the HTML.
How do you resolve this issue?
Add a <html amp> tag on the AMP page (<html ⚡> can also be used, interchangeably):