The Core Difference in One Sentence
A 301 redirect moves both users and search engines from one URL to another permanently, making the original URL inaccessible. A canonical URL tag tells search engines which version of a page is the 'master' copy without moving anyone anywhere — the original URL still loads normally.
The redirect is an HTTP-level instruction; the canonical is an HTML-level hint. That distinction drives every practical difference between the two. One controls access; the other controls attribution. Ecommerce stores need both tools, but conflating them causes ranking losses, duplicate-content penalties, and crawl budget waste.
How Each One Works Mechanically
When a browser or crawler requests a URL with a 301 redirect, the server returns an HTTP 301 status code plus a Location header pointing to the destination. The original URL ceases to exist as a functional endpoint. Google treats the redirect as a signal to consolidate link equity to the destination and eventually drops the redirected URL from its index.
A canonical tag lives inside the HTML <head> of a page: <link rel='canonical' href='https://example.com/preferred-url' />. The page still renders and responds with a 200 OK status. Google reads the tag as a strong recommendation — not a command — to attribute indexing signals to the canonical URL rather than the page it found the tag on. Duplicate pages can still be crawled and cached even with a canonical in place.
The mechanical gap matters for ecommerce. A product page with UTM tracking parameters (e.g., ?utm_source=email) returns a full 200 response with a canonical pointing to the clean URL. No redirect is needed because the page content is identical; the canonical handles consolidation. But a discontinued product URL that now maps to a successor product requires a 301 because the original URL should no longer resolve at all.
When to Use a 301 Redirect vs a Canonical Tag
Use a 301 redirect when the original URL should stop existing: site migrations, domain changes, deleted product pages redirected to category pages, HTTPS enforcement, or www-to-non-www consolidation. The redirect is the right tool when leaving the old URL live would confuse users or fragment link equity across two genuinely different destinations.
Use a canonical tag when the same (or near-identical) content is accessible at multiple URLs that all need to stay live. Ecommerce examples include faceted navigation URLs (/shoes?color=black&size=10), session IDs appended to URLs, printer-friendly page variants, and product pages syndicated to third-party retailers. The canonical tells Google which URL to rank without breaking the others.
A practical rule: if users should never land on the old URL, use a 301. If users legitimately land on multiple URLs showing the same content, use a canonical. The wrong choice in either direction creates problems — a canonical on a deleted page returns a 404, not a redirect; a 301 on a parameterized URL breaks filters that legitimate shoppers use.
How They Interact — and Where They Conflict
Google's crawlers follow 301 redirects before reading canonical tags. If URL A redirects to URL B, and URL B has a canonical pointing to URL C, Google consolidates signals to URL C. Chains like this inflate crawl budget consumption and slow equity transfer, but they do resolve eventually. The redirect takes precedence because it happens at the HTTP layer before any HTML is parsed.
Conflict arises when a page carries a self-referencing canonical (pointing to itself) but is also the target of a redirect from another URL. That is normal and correct — the destination of a 301 should carry a self-canonical to confirm it is the authoritative version. Problems appear when the redirect destination has a canonical pointing back to the redirected URL, creating a loop that Google resolves unpredictably.
For ecommerce stores running both redirects and canonicals at scale — common after platform migrations — audit for redirect chains, redirect loops, and canonicals pointing to non-200 URLs. Tools like Screaming Frog surface these mismatches quickly. A canonical that targets a URL returning a 301 is a wasted tag; Google ignores canonicals pointing to redirects and makes its own consolidation decision.
Side-by-Side Comparison for Ecommerce Decisions
HTTP status code: 301 returns a 301 response; canonical returns 200. User experience: 301 redirects the browser to a new URL; canonical keeps the user on the requested URL. Search engine behavior: 301 consolidates and eventually removes the old URL from index; canonical consolidates but leaves all URLs crawlable. Reversibility: 301 redirects are permanent by definition but technically reversible in server config; canonicals are easy to update in HTML at any time.
Link equity transfer: both 301 redirects and canonical tags pass link equity to the destination/canonical URL, but 301 redirects do so with higher certainty because they are HTTP commands rather than HTML hints. Indexation: the redirected URL drops from Google's index over time; canonicalized duplicate URLs typically do not appear in search results but remain in Google's crawl queue. Crawl budget impact: each 301 adds a hop; canonicalized URLs still consume crawl budget when Googlebot visits them.
Actionable Decision Framework
Before implementing either solution, answer two questions: (1) Should this URL ever return a 200 response again? If no, use a 301 redirect to the most relevant live URL. (2) Does this URL show substantially the same content as another URL that must stay live? If yes, add a canonical tag pointing to the preferred version.
For ecommerce stores specifically: implement HTTPS and www/non-www consolidation via server-level 301 redirects, not canonicals — these are access-control decisions. Handle parameterized URLs (sort, filter, tracking) with canonical tags pointing to the clean base URL. When retiring a product, 301 redirect to the closest available substitute or the parent category. After any platform migration, audit every redirected URL to confirm the destination carries a correct self-referencing canonical.
Neither tool substitutes for the other. Using a canonical where a 301 belongs leaves a dead URL live, fragmenting equity. Using a 301 where a canonical belongs breaks functional filter URLs and harms site usability. Treat them as complementary tools with distinct jobs, not interchangeable fixes for duplicate content.