in-browser mode, nothing uploaded

Or paste the HTML. We read it here.

Paste your page source, or just the <head>, and we pull out every rel="canonical" and evaluate it in your browser. Nothing is sent anywhere. Add your page's real URL and we can also tell you whether the canonical points at this page or somewhere else.

what a canonical checker should catch

One clean signal, or none. Never a contradiction.

Google treats the canonical tag as a strong hint about which URL to index and credit. The failures are rarely a missing tag; they are contradictory or misdirected tags that quietly send your ranking signals to the wrong place. Here is what we read, all grounded in Google's Consolidate duplicate URLs guidance.

Self-referencing vs cross-domainMost pages should point their canonical at themselves. A canonical pointing at a different domain tells Google that another site is the original, and that page may never rank. We compare the canonical's host to the page's host and call it plainly.
Conflicting canonical signalsTwo canonical tags with different URLs, or an HTTP Link header that disagrees with the HTML tag, cancel each other out. Google's guidance is that mixed signals get discarded, so it picks a version for you. One page, one canonical.
Relative and fragment URLsGoogle recommends absolute canonical URLs. A relative path invites path-resolution mistakes, and a URL with a #fragment gets stripped, so the canonical you think you set is not the one Google reads.
Protocol and index contradictionsAn HTTPS page that canonicalizes to its HTTP twin hands the vote to the insecure duplicate. A page that is both noindexed and canonicalizes elsewhere sends two conflicting removal signals, which Google's docs warn against.
The tag lives in the headA canonical outside <head> is ignored entirely. We confirm it is where Google will actually look for it.

canonical questions, answered straight

The honest version.

What is a self-referencing canonical and do I need one?

A self-referencing canonical is a rel="canonical" tag that points a page at its own URL. It is not strictly required, and Google can pick a canonical without one, but it is a low-risk best practice: it states your preferred address clearly, which helps when the same page is reachable with tracking parameters, trailing slashes, or www and non-www variants. The safe default for a normal page is a canonical pointing at its own clean, absolute URL. The exception is a page that is genuinely a duplicate of another, which should canonicalize to the original.

Does the canonical tag force Google to index that URL?

No. The canonical is a hint, not a command. Google considers your canonical alongside other signals, redirects, internal links, sitemaps, and the HTTPS version, and it can choose a different URL than the one you declared. That is why contradictions are so costly: if your canonical, your redirects, and your sitemap disagree, Google resolves the conflict on its own. To keep a page out of the index entirely, use a noindex meta tag, not a canonical, and never combine noindex with a canonical that points elsewhere.

Can a wrong canonical tag hurt my rankings?

Yes, and it is one of the quieter ways to lose visibility. A canonical pointing at your homepage from every page tells Google those pages are duplicates of the homepage, so they may drop out of results. A canonical pointing at another domain hands your ranking signals to that site. Because the page still loads normally for visitors, the mistake is invisible until you check the tag. Point each page's canonical at its own preferred URL unless it is truly a duplicate, and verify it with a checker rather than trusting that the template got it right.

one check of the whole picture

Canonical is one signal. We read the other 111.

A clean canonical keeps your ranking signals where they belong. Whether Google and the AI engines can reach, read, trust and cite the whole page is a bigger question, and it is the one the full AuditLamp audit answers: 116 documented checks across search, answer boxes and AI assistants, ranked by what is costing you the most. Full score on screen, no email taken.