Do your HTTP and HTML canonicals disagree?

By Matt Kerr·Published 11 November 2026

It compares a canonical in the response header with the canonical in the HTML.

What Check Engine measures

The page must be intended for search and have a canonical in both its HTTP Link header and its HTML. Its header address is resolved against the page URL. Both targets have trailing slashes removed before comparison. Different targets produce a conflict. A page with only an HTML canonical produces no conflict here.

The check reads the saved HTTP headers and HTML canonical values. A server or proxy may add a header separately from the page template. Inspect both places before editing.

How to read the result

Conflicts are high severity. The report gives a source page and both targets so that the server configuration and page template can be reviewed together instead of guessing which layer supplied the wrong value.

Why it matters

Separate configuration layers can make separate claims for the same response. A correct-looking tag in page source does not reveal a conflicting HTTP header, which explains why looking at the browser document alone can miss this test.

How to fix it

Choose the intended canonical destination. Align the server or proxy header with the HTML tag. Check every layer that can add a declaration. Request the page again and inspect both values in the new response.

How to fix conflicting canonical tags

What we found in field audits

Problems in Crawlability & indexing were found on 12 of the 14 sites we audited. These are area totals. Read the field-audit method.

Method note

backend/seo_engine/checks/international.py, canonical_conflict, revision 0bb8e8d3.