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Friday, June 17, 2011
Based on your feedback, we’re happy to announce that Google web search now supports
linkrel="canonical" relationships
specified in HTTP headers as per the syntax described in
section 5 of IETF RFC 5988.
Webmasters can use rel="canonical" HTTP headers to signal the canonical URL for both
HTML documents and other types of content such as PDF files.
To see the rel="canonical" HTTP header in action, let’s look at the scenario of a
website offering a white paper both as an HTML page and as a downloadable PDF alternative, under
these two URLs:
https://www.example.com/white-paper.html
https://www.example.com/white-paper.pdf
In this case, the webmaster can signal to Google that the canonical URL for the PDF download is
the HTML document by using a rel="canonical" HTTP header when the PDF file is
requested; for example:
GET /white-paper.pdf HTTP/1.1
Host: www.example.com
(...rest of HTTP request headers...)
HTTP/1.1 200 OK
Content-Type: application/pdf
Link: <https://www.example.com/white-paper.html>; rel="canonical"
Content-Length: 785710
(... rest of HTTP response headers...)
Another common situation in which rel="canonical" HTTP headers may help is when a
website serves the same file from multiple URLs (for example when using a content distribution
network) and the webmaster wishes to signal to Google the preferred URL.
We currently support these link header elements for web search only. As we see how webmasters are
using these elements, we're hoping to add support for them in our other properties. For more
information, please see our Help Center articles about
canonicalization and the
rel="canonical" element.
If you have any questions, please ask in our
Webmaster Help Forum.
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Missing the information I need","missingTheInformationINeed","thumb-down"],["Too complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],[],[[["Google web search now supports `rel=\"canonical\"` relationships specified in HTTP headers, allowing webmasters to indicate the preferred URL for a piece of content."],["Using `rel=\"canonical\"` in HTTP headers enables webmasters to signal the canonical URL for various content types, including HTML documents and PDF files."],["This feature is particularly helpful for situations like offering alternative file formats or serving the same content from multiple URLs, like with a CDN."],["Currently, `rel=\"canonical\"` HTTP header support is limited to web search, but Google may expand support to other properties in the future."]]],["Google web search now supports `rel=\"canonical\"` relationships specified in HTTP headers, as defined by IETF RFC 5988. Webmasters can use these headers to indicate the canonical URL for HTML and other content types like PDFs. For example, a PDF's canonical URL can be designated as an HTML page. This helps when content exists on multiple URLs, such as with content distribution networks, signaling a preferred URL to Google. This feature is currently limited to web search.\n"]]
