Could massive redirects to the homepage during a site merger be an SEO trap?

Why does Google mention 'soft 404s' in this context?

A soft 404 refers to a page that returns an HTTP 200 or 301 code but offers no relevant content related to the original URL. When you redirect 500 blog articles to your homepage, Google considers these redirects provide no contextual value to the visitor.

The engine then treats these redirects as soft errors, just as if the pages had disappeared. As a result, you lose the link juice passed along, the acquired positions, and potentially part of your indexing history. Google does not directly penalize but simply ignores the redirect signal.

What does 'contextual continuity' really mean?

Contextual continuity involves matching each old piece of content with a thematically equivalent one on the new domain. An article on 'how to choose running shoes' should point to similar content, not to the generic 'Sport' category or the homepage.

This approach preserves the semantic graph that Google has built around your content. Entities, lexical co-occurrences, and topical relationships remain coherent. Without this continuity, you break the connections that the engine has woven over months or years.

How does this differ from a classic migration?

In a classic domain migration, you move your site exactly as is: same architecture, same URLs (with a few adjustments). A site merger poses a different challenge as you integrate two distinct content universes.

You need to decide which content to merge, which to keep separate, and which to abandon. This last point creates risk: if you choose the easy route by redirecting everything to the homepage, Google interprets this as a mass abandonment of content rather than a strategic merger.

• Contextual 1:1 redirect: maintains link equity and positions
• Mass redirect to homepage: treated as soft 404, SEO signal loss
• Mandatory prior analysis: identify a relevant equivalent on the merged domain for each old article
• Case of orphaned content: plan a specific strategy (301 to a close category, or a true 410 Gone if obsolete)
• Impact timeline: effects are measured over 3 to 6 months, not immediately after the merger

Is this approach consistent with what we observe on the ground?

To be honest, Mueller's statement precisely aligns with what post-merger audits reveal. Sites that chose the easy solution — redirecting everything to the homepage — consistently experience an organic traffic drop of 40 to 70% within 3 months of the merger.

What is more interesting is that Google does not publicly communicate about the tolerance threshold. How many redirects to the homepage can we afford before the engine decides it’s an abusive pattern? [To verify] in the absence of quantified data, it is recommended to limit these redirects to less than 5% of the total volume.

What nuances should be considered based on context?

Not all content is created equal. An article that generated no organic traffic in 12 months and has no backlinks can be sacrificed without major impact. In this case, a 301 to the parent category or even a 410 Gone (permanent removal) is preferable to an artificial redirect.

The situation is radically different for content that capitalizes on external link juice. An article with 20 quality backlinks must absolutely find a relevant contextual destination, even if it means creating a new summary content on the merged domain.

What to do about duplicate content between the two sites?

This is the most common scenario: the two merged sites covered similar topics, inevitably creating thematic duplicates. Redirecting the old article to the new one that covers the same topic seems like the obvious solution, but it hides a trap.

If the content of the absorbed site was better positioned or more complete, redirecting it to a lower version risks creating friction in the algorithm. Google will compare the old content (via its cache) with the destination of the 301. If the destination is objectively weaker, the transfer of authority will not occur fully. In these cases, it is essential to enhance the destination page before implementing the redirect.

How to effectively map redirects before a merger?

First essential step: extract the complete inventory of both sites with their respective SEO metrics (12-month organic traffic, number of backlinks, average positions). A Screaming Frog or Oncrawl crawl combined with Search Console and Ahrefs/Semrush data is the bare minimum.

Then, build a thematic matching matrix. For each URL of the site to be absorbed, identify the best match on the main domain based on three criteria: semantic similarity, authority level, and internal linking architecture. This manual phase is time-consuming but irreplaceable.

What to do with orphaned content that has no relevant equivalent?

You will inevitably have content that finds no natural match on the merged domain. Three options are available depending on the orphaned content profile.

Option 1: if the content has authority (backlinks, traffic), recreate equivalent content on the main domain before implementing the 301. Option 2: if the content is moderate but thematically close to an existing category, redirect to that category. Option 3: if the content is obsolete or of no value, use a 410 Gone code rather than a false redirect.

How to check whether the merger has not created soft 404s?

Monitor three indicators in the 3 months post-merger. First signal: a sudden drop in the number of indexed pages in the Search Console without a corresponding increase on the main domain. Second signal: a drop in organic traffic greater than the sum of the two sites prior to the merger.

Third signal, more subtle: an increase in soft 404s in the Search Console coverage report. If Google flags pages from the new domain as soft 404 when they are supposed to be the destinations of your redirects, it indicates that contextual mapping has failed.

• Crawl both sites and extract all SEO metrics (traffic, backlinks, positions)
• Create a URL-by-URL thematic matching matrix with similarity scores
• Identify orphaned content and decide: recreate, redirect to category, or 410 Gone
• Implement redirects in progressive waves to monitor impact
• Daily check the Search Console: indexed pages, soft 404s, organic traffic
• Verify the HTTP status of redirects in production with a dedicated tool (Screaming Frog, Oncrawl)