Canonical Checker

About Canonical Checker

Paste a page URL and click Analyze. We read link rel=canonical in the HTML and Link rel=canonical in the HTTP headers. Missing canonical is a warning. Multiple canonicals or an invalid URL are critical. A relative canonical is a warning. Host or protocol mismatch with the URL you asked us to fetch (www stripped) is flagged. A cross-domain canonical is a notice; syndication sometimes uses that on purpose.

We then fetch the canonical target, following up to five redirects. If the target still looks like a redirect, you get Canonical points at a redirect. Status 400 or higher on the target is critical. noindex on the target (meta robots or X-Robots-Tag) is critical. A 301 that already landed on 200 looks like a healthy destination because redirects were followed.

When to use it

Use it after a plugin or theme adds a second link rel=canonical, or after you change trailing slashes, HTTPS, or www and the old href is still baked into the head. That is when two preferred URLs fight.

Also use it when Indexability already said the canonical points away, and you need the target fetched: does that preferred URL 404, still redirect, or carry noindex.

How to use Canonical Checker

1. 1Enter the page URL. Use the URL you expect search engines to see.
2. 2Click Analyze. We may fetch the canonical target as well as the page.
3. 3Read the flags. Each row has a why line and a fix line.
4. 4Align the CMS canonical. One absolute, self-referencing canonical is the usual happy path.

How to read the results

The line under the form lists every canonical we found, joined with a middle dot, including a Link header value if one exists. Then the issue list. Critical: multiple tags, an invalid URL, the target returned 400 or higher, or the target is noindex. Warning: missing tag, a relative href, host or protocol mismatch, or the target still looks like a redirect after five hops.

Cross-domain is a notice (syndication can be intended). Canonical looks consistent is the happy path. example.com is No canonical tag. Wikipedia Main_Page is a self-absolute pass. www.iana.org points at https://iana.org/ and shows Cross-domain canonical plus that pass row.

Why this matters

Crawlers treat the canonical href as the URL that should receive the signals. If this page points elsewhere, this URL is the one that drops from the index in favor of the target. That is useful for true duplicates and fatal when the target is a 404 or a noindex document.

Two canonicals in one response are worse than none: the signals conflict and both may be ignored. A relative href is easier to resolve against the wrong base. A target that still redirects means the preferred URL is not the final document.

Limits and privacy

One public URL, then a second fetch of the preferred href (up to five hops). Loopback and reserved IPs are rejected. Tags written only after paint are missed. About 20 paired fetches per minute on your network. No login.

Common mistakes

Reading Canonical looks consistent as proof Google picked this URL. It means the tag and the target fetch agreed on this run.

Pasting the www host when the tag names the apex. You will see host mismatch or Cross-domain even when the live site is fine on the other host.

Stopping at Indexability's Away chip. This page is the one that fetches the target and can show Canonical returned 404 or Canonical target is noindex.