Does blocking redirects in robots.txt really eliminate their SEO impact?

Why isn’t blocking a redirect enough?

The robots.txt file prevents Google from crawling a URL but does not remove the link information itself. When Googlebot discovers an external link pointing to your site, it registers that link signal even if it cannot follow the redirect.

Specifically, if a third-party site points to example.com/old-page which redirects to example.com/new-page, and you block /old-page in robots.txt, Google still sees the initial signal from the external link. It just cannot verify where the redirect leads.

What’s the difference with the nofollow attribute?

The nofollow attribute explicitly tells Google not to pass any authority through that link. Unlike robots.txt blocking that merely prevents crawling, nofollow acts as a link handling instruction.

Google can still discover the target URL of a nofollow link, but it will not pass PageRank or ranking signals. It’s a semantic directive rather than a technical barrier.

When does this distinction become critical?

During a site migration, some SEOs temporarily block old URLs in robots.txt thinking they neutralize unwanted links. This is a mistake: toxic backlinks or misconfigured redirects continue to affect the link profile.

In negative SEO, an attacker may create thousands of spam redirects pointed at your domain. Blocking them in robots.txt does not deactivate the association of these shady domains with yours in Google’s index.

• Robots.txt blocks crawling but not discovery or registration of links
• The nofollow attribute remains the only way to explicitly tell Google to not pass authority
• Redirects blocked in robots.txt can retain their potential relevance in the future according to Google
• This rule particularly applies to complex migrations and negative SEO situations

Does this logic hold true based on field observations?

Yes, and this is actually a point that is often misunderstood. I have seen websites lose up to 30% of their organic traffic after blocking URLs receiving powerful backlinks in robots.txt, thinking they were 'cleaning up' their profile. The result? Google continued to see those links as relevant but could no longer crawl the redirects.

The crawl budget then gets wasted on repeated attempts to crawl blocked URLs. Worse, link signals remain unclear in the algorithm: Google knows a link exists but cannot validate where it leads or if the destination is legitimate.

When should you really use nofollow instead of robots.txt?

Honestly, as soon as an external link points to a redirect that you control. If you manage a site with multiple URL variants (parameters, trailing slash, inherited redirects), blocking them in robots.txt creates more problems than it solves.

However, and this is where Google remains deliberately vague [To be checked], we don’t know exactly how long a blocked link retains its 'potential relevance in the future'. Six months? A year? Indefinitely until the source page disappears? No official data available on that.

In what scenarios does this rule not really apply?

If you block a redirect that no one knows about and has never received any external links, the impact is zero. Google will never discover that link, hence there is no signal to preserve.

Similarly, purely technical internal redirects (such as www/non-www normalization) do not require nofollow. Robots.txt may suffice if the goal is merely to avoid crawling duplicates, not to neutralize backlinks.

What should you concretely do with existing redirects?

First action: audit all redirects blocked in your current robots.txt. Use Screaming Frog or a similar crawler to identify URLs in 301/302 that appear in the robots.txt file.

For each blocked redirect, check in Google Search Console or Ahrefs if it receives external backlinks. If it does, remove it from robots.txt and let Google crawl the redirect normally. The juice will pass correctly.

How to manage unwanted links or negative SEO?

If spammy domains redirect to your site, robots.txt will not protect you. The only solution remains the disavow file in Google Search Console, however imperfect it may be.

For links you control on other sites (dubious partnerships, old site networks), add the rel="nofollow" attribute directly in the HTML. It’s cleaner and more transparent for Google than a robots.txt block that leaves ambiguity.

What mistakes should you absolutely avoid during a migration?

Never block old URLs in robots.txt during a migration. It guarantees the loss of link equity accumulated on those pages. Google needs to be able to crawl the 301s to transfer signals.

Some technical teams reflexively block 'obsolete' URLs to 'force' Google to see only new ones. The catastrophic result: backlinks remain tied to the old URLs that Google can no longer evaluate, and the new pages start from scratch.

• Remove all redirects from robots.txt except those without any external backlinks
• Ensure that the 301s point to active and relevant pages
• Use rel="nofollow" for questionable outgoing links you control
• Monitor toxic backlinks with a third-party tool and use disavow if necessary
• Test the crawling of redirects in Google Search Console after the robots.txt modification
• Document each blocked redirect with its business justification