In short
What it checks
four pieces of evidence: canonical present, canonical valid, conflict between the canonical and the analyzed URL, and multiple canonicals on the same page.
Benchmark
Google asks for an absolute URL, inside head, and recommends that the canonical page declare itself.
Why it matters
Google consolidates the signals of all copies, such as the links they receive, into the canonical URL; if you don’t declare it, Google chooses.
Severity in Wakaris
Critical. Fails on 16% of the pages analyzed.
What this finding is and what it checks
The same page often exists at several addresses without anyone intending it: with http and with https, with www and without it, with tracking or sorting parameters, with or without a trailing slash. To the search engine these are different URLs with the same content: duplicates. Google calls the process of choosing the representative URL of that set canonicalization.
The canonical URL is that representative address. Google defines it as the URL of the page it has chosen as the most representative of a group of duplicate pages. You can tell it your preference with a link rel="canonical" tag in the HTML head, pointing to the address you want treated as official.
This finding shows up when that declaration is missing, badly built, points to an address other than the one analyzed or appears more than once. These are four different situations, and Wakaris separates them into four pieces of evidence.
How it’s checked
Wakaris loads the URL you give it and reads its head looking for rel="canonical" tags. With what it finds, it evaluates four things. Whether the tag is present. Whether it’s valid: Google asks for absolute paths, with protocol and domain, and a relative path like /vestidos/verde.html is its example of what not to do; a malformed URL doesn’t work either. Whether there’s a conflict between the declared canonical and the analyzed URL, that is, whether the page says its official version is a different one. And whether there are several canonical tags, identical or different.
The report returns the result of each piece of evidence with the code snippet from the head, so you can see the tag exactly as it’s written.
One clarification: a canonical pointing to another URL isn’t an error in itself. It’s what a copy with parameters should do to point to the clean version. It deserves a review when the analyzed page should be the official one and yet gives up its place to another. Wakaris flags it for you; deciding which one is official is up to you.
Why it matters
It matters because a page’s signals, above all the links it receives, get split among its copies if nobody says which one is official.
Google lists four reasons to declare the canonical. To specify which URL you want people to see in search results. To consolidate the signals of each copy, such as the links pointing to them, into a single preferred URL. To simplify tracking metrics. And to avoid spending crawl time on duplicates: the canonical page is crawled more often and the duplicates less.
If you don’t declare it, Google decides for you. Its documentation says so plainly: if you don’t specify a canonical URL, Google will identify which version is objectively the best for search. And it adds that, even when declared, it may choose another one because of content quality or technical signals. The tag is a strong signal, not an order; without it you hand over the whole decision.
And what doesn’t happen: Google states that some duplicate content is normal and doesn’t violate its spam policies. The problem isn’t a penalty, it’s dilution.
Common causes
The causes range from not having thought about it to having done it wrong on autopilot.
The first is absence: the template doesn’t generate the tag and nobody adds it. It’s common on small websites and hand-built pages. As long as the site opens with and without www, with http and https, each version competes with the others.
The second is a relative path. Someone writes /producto/123 instead of the full address. Google asks for absolute paths so there’s no ambiguity about domain and protocol.
The third is duplicate canonicals. It happens when two tools think they’re in charge of the tag: the theme adds one and an SEO plugin adds another. If they match, it’s noise; if they differ, the page contradicts itself and the signal is no longer unambiguous.
The fourth is an inherited conflict: a canonical copied from another page, one still pointing to an old domain after a migration, or one that points to the first page on every page of a listing. The page gives up its place without anyone having decided it.
How to fix it
Start with the Wakaris report: it tells you which of the four pieces of evidence fails and shows you the tag exactly as it is in the head. From there, the fix depends on the case.
If it’s missing, add a link rel="canonical" tag in the head with the absolute URL of the official version. Google recommends that the canonical page itself carry a canonical pointing to itself, so on most pages the correct value is its own address, in its clean form.
If it’s relative or invalid, replace it with the full address, with protocol and domain. First choose a single form of the domain, with or without www, and use it in every canonical; MDN also recommends a 301 redirect from the form you didn’t choose to the one you did.
If there are several, find which component generates each one and keep just one. If there’s a conflict, decide which is the official version of that content and make the tag reflect it. Then run the page through Wakaris again and check that all four pieces of evidence are clean.
HTML head with a correct link rel canonical tag, with an absolute URL, next to three incorrect versions: relative, duplicated and pointing to another page
Brief for generating the image
Editorial illustration for a Wakaris technical guide. Topic: HTML head with a correct link rel canonical tag, with an absolute URL, next to three incorrect versions: relative, duplicated and pointing to another page. Style: white background with a soft lime→pale green wash (#F8F7D6 → #E2F2DC), green→lime gradient accent (#8ED390 → #DCD86F), near-black ink (#12150B), pill shapes and rounded corners, soft shadows, clean schematic look, no photography. Format: 16:9, 1440 pixels wide. No legible text: any label, code or figure is shown as gray placeholder bars. The caption carries the meaning, not the image. No real logos or third-party brands. No recognizable people. Tags: url, canonical, head, html, tag, link, rel, canonical
Ask your AI
If you want to dig deeper into your specific case, copy one of these two prompts and paste it into the AI you use. Pick the one that fits your situation.
I already have the finding measured with Wakaris and want to fix it
Act as a professional, careful technical web reviewer. Your goal is to help me understand a specific finding about my website and decide what to do about it, without making anything up. Context: I got this finding from Wakaris, a tool that analyzes a website across 9 areas (performance, SEO, security, social, market, AI, user experience, accessibility and legal) and explains each problem so that every profile on a team can understand it. The finding is: Canonical URL. My page doesn’t declare its canonical URL, the official address of its content, properly: the rel="canonical" tag is missing, isn’t valid, points to another address or appears more than once. Benchmark: a single rel="canonical" tag in the head, with an absolute URL, pointing to the official version of the page (usually the page itself). Paste the Wakaris result here: which evidence fails (missing, invalid, conflict with the analyzed URL or several canonicals), on which page and the tag’s code snippet. If you don’t have it, tell me and I’ll tell you how to get it before we continue. Rules you must follow at all times: 1. Don’t assume anything about my website. Every piece of data you use must come from what I confirm to you or from what Wakaris has measured. If you don’t know something, ask me before stating it. 2. Before giving me any conclusions, ALWAYS ask me these questions, all together and in plain language, to find out whether this finding really affects me and where: a) What platform is your website built on? (WordPress, Shopify, custom-built, other) b) Which evidence failed: the tag is missing, it’s relative or invalid, it points to another address, or there are several? c) If it points to another address, is that address the same page in another form (with www, without parameters) or a different page? d) Do you use an SEO plugin or module besides the theme? Do you know which one generates the canonical? e) Can the website be opened with and without www, and with http and https? Does any of those forms redirect to the other? f) Has there been a domain or URL structure migration recently? g) If a technical fix is needed, would you do it yourself, or would an in-house technician or an agency do it? 3. Every statement or recommendation must be justified in terms of MY context, not in general. If you recommend something, explain why it applies to my case. 4. Always state your level of certainty. If something is a hypothesis because you can’t measure it, say so: you can’t see my website, you’re reasoning from what I tell you. 5. Don’t suggest irreversible or risky technical changes (server configuration, deleting resources, direct changes in production) without first warning me about the risk and that a backup or a test environment is advisable. 6. If you need data that can only be obtained by checking the website (confirming the actual result, the exact page, or whether the fix worked), tell me and recommend that I run the page through Wakaris again: that gets checked, not guessed. 7. The final decision is mine, not yours. Your role is to help me understand and prepare the action, not to decide for me. 8. If the fix goes beyond what I can do myself, or a team will carry it out, help me get the problem ready to hand over: what it is, where it is, why it matters and what should be done, in a format that person can act on. Source of this finding: https://www.wakaris.com/en/guides/seo/canonical-url To check it or check it again: https://www.wakaris.com/ Start by briefly introducing yourself in your role and asking me the first set of questions.
I haven’t measured it yet and want to check whether my website has this problem
Act as a professional, careful technical web reviewer. I’m looking into whether my website has a specific problem, and I want you to help me find out honestly, without taking it for granted. Context: I came to this through Wakaris, a tool that analyzes a website across 9 areas (performance, SEO, security, social, market, AI, user experience, accessibility and legal) and explains each problem so that every profile on a team can understand it. The problem I want to look into is: Canonical URL. The canonical URL is a page’s official address when its content can be reached through several addresses; it’s declared with a rel="canonical" tag in the head. The problem is when that tag is missing, isn’t valid, points to another address or appears more than once. I DON’T know yet whether my website has it: I want to find out. Rules you must follow at all times: 1. First and most important: this is CHECKED on the real page, and you can’t check my website from this conversation. Make it clear from the start that you won’t be able to give me a definitive "yes, you have it" or "no, you don’t", only a hypothesis based on what I tell you. 2. Don’t assume anything. Before giving me any assessment, ALWAYS ask me these questions, all together and in plain language, to estimate whether I’m likely to have the problem: a) Can your website be opened with and without www? And with http and https? Do you know whether one form redirects to the other? b) Do you have pages with filters, sorting or parameters in the address (?sort=price, ?utm_...)? c) Do you use a theme or template and also an SEO plugin or module? d) Have you ever changed your domain or address structure? e) What platform is the website built on? (WordPress, Shopify, custom-built, other; or I don’t know) f) Has anyone ever set the "canonical URL" in your CMS, or do you not know what it is? 3. Based on my answers, give me a clear estimate of whether it’s LIKELY or UNLIKELY that I have it, justified by what I’ve told you and explicitly marked as a hypothesis, not a diagnosis. 4. Tell me directly that the only way to really know is to check it, and that I can do it for free and without creating an account by running my website through Wakaris, which will give me the actual result, the status of the four checks, with the tag exactly as it’s written and, along the way, the status of the other areas. 5. If I ask you how to check it by hand, don’t hide it from me, but remind me that Wakaris does it faster, on the real page and with extra information I don’t get by hand. 6. If, once checked, it turns out I do have it, tell me the next step is to understand how it affects me and how to fix it in my specific case. 7. The conclusion and the decision are mine, not yours. You help me find my way. Source of this finding: https://www.wakaris.com/en/guides/seo/canonical-url To check it: https://www.wakaris.com/ Start by briefly introducing yourself in your role, making point 1 clear, and asking me the set of questions.
Frequently asked questions
Do all pages need a canonical tag, even if they have no copies? +
Google doesn’t require it: it says a site will work fine without declaring a preference and that, if you don’t declare one, it chooses. But it recommends that the canonical page point to itself, and almost every page has copies you don’t see: with parameters, with and without a trailing slash. Declaring it gives you control.
Can the canonical point to another domain? +
Yes. Google says rel="canonical" is used to indicate the preferred version among duplicates, and that version can be on another domain, for example when the same content is published on two sites. What Wakaris flags as a conflict is the analyzed URL giving up its place to another; if that’s intentional, there’s nothing to fix.
Why does Google show a URL different from the one I declared as canonical? +
Because the tag is a strong signal, not an order. Google documents that, even if you explicitly designate a canonical page, it may choose another one for reasons such as content quality or technical signals. It usually happens when the canonical contradicts other signals: redirects, internal links or a sitemap pointing to another version.
Does duplicate content penalize my website? +
Not in the sense of a penalty. Google states that some duplicate content on a site is normal and doesn’t violate its spam policies. The real cost is different: signals get split among copies, crawling is spent on repeated pages and the search engine may show the version you didn’t want.
Sources cited
- developers.google.comHow to specify a canonical with rel="canonical" and other methods, Google Search Central: reasons to declare the canonical, absolute versus relative paths, the tag is only accepted in
head, self-referencing canonical and what happens if you don’t declare it. - developers.google.comWhat is URL canonicalization, Google Search Central: definition of canonicalization and canonical URL, how duplicates arise, more frequent crawling of the canonical and duplicate content as something normal that doesn’t violate spam policies.
- developers.google.comFix canonicalization issues, Google Search Central: Google may choose a canonical different from the declared one because of content quality or technical signals.
- developer.mozilla.orgChoosing between www and non-www URLs, MDN Web Docs: choosing a single canonical domain, redirecting the other one with a 301 and using
link rel="canonical"to tell search engines where the page lives.
Updated: September 7, 2026.
This article is part of Wakaris, which analyzes your website across 9 areas and explains each finding so that every profile on your team can understand it.