Does the 301 really determine which URL Google will canonize?

What does Google mean by "strong signal but not determinative"?

Google qualifies the 301 as a strong signal, meaning it carries significant weight in the canonical selection algorithm. However, this wording also implies that there are other signals—sometimes conflicting—that Google evaluates in parallel.

In reality, Google combines several indicators: the canonical tag, internal links, external links, the XML sitemap, indexing history, and even URL structure. If these signals conflict, Google arbitrates according to a logic that remains largely opaque.

Why doesn’t Google always follow a 301?

A common scenario: you migrate a site with 301s, but your internal links continue to point to the old URLs. Google sees a conflict between the 301 (which states “go to B”) and the internal linking (which asserts “A is the true page”).

Another classic scenario: the XML sitemap still contains the old URLs, or worse, both versions. Google then receives conflicting signals and may decide not to follow the 301 if other indicators are more consistent in the opposite direction.

What other canonization factors does Google evaluate?

Google considers the age of the URL, its crawl history, the quality and consistency of the content, and the presence of backlinks pointing to a specific version. If URL A receives 90% of the backlinks and the 301 points to B, Google may legitimately hesitate.

The canonical tag is another explicit signal, often considered more reliable than a 301 if it is consistent with the rest. And Google always favors HTTPS URLs over HTTP, and versions without trailing slashes if they are crawled more frequently, etc.

• The 301 is a strong signal but not absolute—Google arbitrates between multiple canonization indicators.
• Signal conflicts (301 vs internal links, sitemap, canonical) can prevent Google from following the redirect.
• Google favors overall consistency: if all signals point to the same URL, it will respect it.
• Backlinks, age, HTTPS protocol also play a role in selecting the canonical URL.
• A successful SEO migration requires aligning all canonization signals, not just the 301s.

Is this statement consistent with real-world observations?

Absolutely. We regularly see cases where Google ignores a properly set up 301 because the internal linking heavily points to the old URL. Or because the XML sitemap has not been updated. Or even because hundreds of backlinks continue to point to the non-301 version.

Google is not lying here: the 301 is a strong signal. But it does not automatically outweigh all other aggregated signals. If you have 10 signals saying "A" and only one 301 saying "B", Google may legitimately choose A. [To be verified]: Google does not publish any numerical weighting, so it’s impossible to know from what threshold the 301 prevails.

In what cases is the 301 not enough to enforce canonization?

The first classic case: redirect chains. If A redirects to B, which redirects to C, Google may decide to bypass and canonize C directly, or conversely, block at B. The behavior is not completely predictable.

The second case: incorrectly typed temporary redirects. A 302 may be interpreted as a weak or contradictory signal if other indicators point to the source URL. And if you switch from a 302 to a 301 afterward, Google may retain the old directive in memory for weeks.

What nuances should be applied to this statement?

Google talks about a "group of URLs" — implying that it detects a cluster of duplicates. If your URLs are sufficiently different (distinct content, divergent structure), Google will not even group them, and the 301 will have no effect on canonization.

Another nuance: the crawl speed. A freshly established 301 may take several weeks to be respected, especially on low crawl budget sites. If Google does not recrawl all the consistent signals (sitemap, internal links, canonical) quickly enough, it will continue to index the old URL.

What practical steps should you take to ensure Google respects your 301s?

First step: align all signals. Update the XML sitemap with the new URLs only. Correct the internal linking to point directly to the target URLs without going through the 301s. Add a canonical tag on the new pages pointing to themselves.

Second step: force the recrawl. Submit the new URLs via Search Console, request a URL inspection on strategic pages. The faster Google crawls the consistency of your signals, the faster it canonizes correctly.

What mistakes should be absolutely avoided?

Never leave redirect chains. If A redirects to B, all internal links must point directly to B. Also, avoid cross redirects (A to B, but an internal link from B to A), which create a signal conflict.

Not updating the XML sitemap is a common mistake. If Google continues to see the old URLs in the sitemap, it crawls them, detects the 301, but receives a contradictory signal about what is "important" to you. The result: unpredictable canonization.

How to verify that Google has indeed canonized the right URLs?

Use the URL inspection tool in Search Console: Google indicates which URL it chose as canonical. If it’s not the one you’re targeting, a contradictory signal persists. Analyze server logs to see if Google continues to heavily crawl the old URLs.

Also, monitor your positions and traffic by URL in Search Console. If the old URL continues to receive impressions/clicks after migration, it is still indexed—an indication that canonization has not occurred.

• Implement clean 301s (no chains, no loops).
• Update the XML sitemap with only the new URLs.
• Correct the internal linking to point directly to the target URLs.
• Add a self-referencing canonical tag on each new page.
• Force the recrawl via Search Console on strategic pages.
• Check the canonical URL chosen by Google via URL inspection.