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  • Writer's pictureBrent Payne

Canonical mismatch between rendered and response HTML

When analyzing a specific URL, one may discover that the canonical tag within the source differs from that in the rendered version of the page.


Why is this important?

The process of rendering a webpage is more complex and time-consuming than simply fetching the source HTML. Due to this, Google adopts a bifurcated approach for crawling: initially, they analyze the response HTML, then proceed to render the page for a secondary evaluation, modifying their index based on the rendered page's content.


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In light of this, delivering inconsistent signals through the source and rendered HTML—for example, in the form of varying instructions on robots directives, canonical tags, and hreflang attributes—may impede proper indexing.


Injecting canonical tags dynamically using JavaScript is inadvisable according to Google's guidance. Should there be a discrepancy between the response and the rendered HTML's canonical tags, search engines might not correctly acknowledge the intended version.


What does the Optimization check?

This Optimization is activated when any internal URL features a canonical tag that is not consistent between the page's response HTML and its rendered state.


Examples that trigger this Optimization

This Optimization is set off by URLs which include a canonical link in the source HTML's head element that differs from the link found in the rendered HTML.


For instance, consider the following response HTML:

<!doctype html><html lang="en"> <head>    <meta name="robots" content="index,follow">    <link rel="canonical" href="https://www.example.com" />    ... </head> <body>...</body></html>


And contrast it with the rendered HTML that appears as:

<!doctype html><html lang="en"> <head>    <meta name="robots" content="index,follow">    <link rel="canonical" href="https://otherexample.com" />    ... </head> <body>...</body></html>


How do you resolve this issue?

Per Google's policy, they disregard the rendered canonical for indexing, thus it is not reliable for such purposes. It is best practice to have a consistent canonical tag present in the HTML source rather than allowing it to alter during rendering.


While Google advises against using JavaScript to manage canonicals, they provide guidance on how to approach it if necessary:

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Further Reading

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