Canonical URL Checker
Compare a page URL with a canonical declaration from a URL, HTML link element or HTTP Link header, then inspect how the scheme, host, path, query and fragment differ.
Canonicalization Is About Consolidating Equivalent URLs
A canonical annotation is useful when several URLs represent the same or substantially similar content: tracking variants, printer views, filtered paths, protocol/host variants or duplicated product URLs. It is not a substitute for deciding which page should actually exist.
Canonical Signals Work Better When the Rest of the Site Agrees
Search engines can consider redirects, sitemap inclusion, internal links, HTTPS and other signals alongside rel=canonical. A page that canonicals to URL A while internal links and redirects consistently favor URL B creates avoidable ambiguity.
HTTP Link Canonicals Need a Real Link-Header Parser
A Link header can contain several comma-separated link-values, and quoted parameter values can themselves contain commas. Splitting the header on every comma can therefore invent fake links. The parser separates link-values only outside URI angle brackets and quoted parameter text, then reads the first rel parameter as RFC 8288 requires.
The HTML Canonical Belongs in the Head
Google accepts the canonical link element from the HTMLhead. It also ignores canonical annotations that carryhreflang, lang, media ortype, because those attributes describe alternate versions. Keep language or device alternatives on their own link annotations.
A Canonical Is a Preference, Not a Command
Google can choose a different canonical when content similarity and other signals disagree with the declaration. Redirects, internal links, sitemap URLs and HTTPS choices are easier to reason about when they all reinforce the same preferred URL.
Fragments and Tracking Parameters Deserve Different Treatment
A fragment identifies a client-side part/state of a document and is not the normal canonical document identifier. Tracking parameters are different: they are valid URL query parameters, but often should not remain in a preferred URL if they only describe attribution rather than content.
A Structurally Valid Canonical Can Still Be Wrong
URL syntax cannot tell whether two pages actually contain duplicate or very similar content. A category page can point cleanly at a product URL and still be the wrong consolidation choice. Compare the content and intent before merging signals across paths or domains.
Current guidance on canonical signals, absolute URLs, HTML-head placement, alternate-version attributes, redirects and sitemap consistency.
Defines canonical as the preferred IRI for duplicative or superset content and explains important misuse cases.
Defines the HTTP Link header serialization, rel parameter handling and link-context rules.