Should you really choose a subdirectory over a subdomain for your microsite?

Why does Google take such a clear stance on this issue?

John Mueller typically does not engage in binary recommendations. When he decides so definitively, it's because the confusion on the ground is massive — and it is. For years, SEOs have debated: subdomain or subdirectory for a corporate blog, a press space, an event site?

Mueller’s answer is decisive: for content linked to the main domain, the subdirectory wins. Why? Because Google treats the subdomain as a quasi-distinct entity in its crawling and ranking system. Each subdomain starts with its own crawl budget, an independent link profile, and separate authority signals.

What does this mean concretely for PageRank and signals?

In a subdirectory, every external link obtained by your microsite directly boosts the authority of the root domain. PageRank flows naturally between /blog and /products via internal linking. This is a massive asset if you're launching editorial content to boost the visibility of a young e-commerce site.

In a subdomain, you fragment your signals. A link to blog.yoursite.com does not mechanically benefit www.yoursite.com. Google has to establish the relationship between the two entities — and nothing guarantees that it will do this effectively. The result: you dilute your SEO potential rather than concentrate it.

In what cases does the subdomain remain relevant?

Mueller cites a specific example: forum vs main site. If your microsite serves a radically different function — community forum, support platform, reseller space — the subdomain is justified. The goal is no longer to pool authority but to isolate content whose nature, audience, or objectives diverge.

Another use case: multilingual or multi-regional sites where the subdomain facilitates technical management (local servers, hreflang, distinct geographic targeting). But beware: Google can crawl and index structures in /fr/ or /en/ without issue — the subdomain is not a requirement.

• Subdirectory: For thematic microsites, blogs, resources, event landing pages linked to the main activity
• Subdomain: For functionally distinct content (forum, support, third-party marketplace, separate web app)
• PageRank Consolidation: The subdirectory pools authority; the subdomain fragments it
• Technical Maintenance: One CMS, one sitemap, one Search Console in subdirectory — versus duplicated management in subdomain

Is this recommendation consistent with what we see in practice?

Yes, overwhelmingly. A/B tests conducted on migrations from subdomain → subdirectory show organic traffic gains in 70-80% of cases, especially for young or moderately authoritative sites. The reason? PageRank stops being compartmentalized. Internal linking becomes effective. The crawl budget concentrates.

But — and this is where Mueller remains cautious — some massive and well-established subdomains (e.g., support.microsoft.com, developers.google.com) perform very well. Why? Because they have amassed their own authority over the years, with independent link profiles. Migrating such a subdomain to a subdirectory would be risky and costly for marginal gain.

What nuances need to be applied to this guideline?

First point: Mueller refers to microsites linked to the main content. If your microsite addresses a related topic but with a distinct editorial positioning, the question becomes more complex. Example: a cosmetics brand launching a lifestyle media subdomain — the goal may indeed be to decouple the image to reach a broader audience without diluting the product brand.

Second point: the question of CMS and technical stacks. If your main site operates on a legacy proprietary CMS and your microsite requires WordPress or a modern stack, the subdomain might be a lesser evil technically. But beware: this is just a band-aid. In the medium term, restructuring the architecture to unify in subdirectory remains preferable if the content is complementary.

Third nuance — which Mueller does not mention: the risks of cannibalization. In a subdirectory, if your microsite targets keywords too close to your main pages without a clear linking strategy, you can create internal conflict. The subdomain isolates this risk. [To be verified]: Google claims to know how to manage intra-domain cannibalization, but real-world observations still show SERP fluctuations on poorly structured sites.

In what cases does this rule frankly not apply?

If you manage a brand network or a group with distinct legal entities, each brand deserves its own root domain — not a subdirectory of the holding site. Example: LVMH will never list Louis Vuitton under lvmh.com/louisvuitton. Here, the subdomain isn't even relevant: it’s an entirely separate domain that stands out.

Another exception: temporary high-budget media campaigns. Launching an event site in a subdomain allows for a clean shutdown after the event without affecting the main structure or multiplying 301 redirects. But if the event is recurring (e.g., annual sales), it’s better to have a permanent /sales in subdirectory.

What should you concretely do if you're launching a new microsite today?

Choose the subdirectory by default, unless there’s a compelling technical or editorial reason. Structure the URL right from the start: /blog, /resources, /events, /press. Avoid unnecessary depth levels: /fr/blog/articles/2024/january — prefer /blog/article-title. The flatter it is, the better for crawl and PageRank.

If your current CMS does not easily allow adding a subdirectory (as with rigid SaaS platforms), challenge this technical choice. A headless CMS or a hybrid architecture (Next.js frontend + API backend) allows you to manage multiple sections under the same domain without infrastructure duplication. It's more complex, but SEO-friendly from the start.

What mistakes should absolutely be avoided during a subdomain → subdirectory migration?

Classic mistake: migrating without cleaning up the internal linking. If your old subdomain pages contain dozens of internal links to other pages of the subdomain, and you redirect everything in bulk, you create redirect chains. The result: diluted PageRank and slowed crawl.

Another pitfall: forgetting to update sitemaps and canonicals. After migration, your sitemap must point to the new URLs in the subdirectory, and each page must have its own canonical. If Google still finds canonicals pointing to the old subdomain, it will hesitate — and you'll lose indexing time.

Third mistake: not monitoring Search Console after migration. Set up a separate property for the subdirectory if necessary, or filter reports to isolate the migrated URLs. Watch for 4xx errors, soft 404s, indexed pages that haven't been submitted. A clean migration takes 4 to 8 weeks for full stabilization — don't let up until then.

How can I check if my site's current structure is optimal?

Run a Screaming Frog or Oncrawl crawl of your main domain and your subdomains. Export the indexed URLs via Search Console. Compare page volumes, link profiles (Ahrefs, Majestic), and traffic performance (GA4). If a subdomain captures less than 10% of the main domain's traffic and addresses a complementary topic, it’s a candidate for migration.

Also analyze the internal linking: how many links connect the subdomain to the main domain? If it’s less than 5-10 strategic links, you already have a segmentation problem. The subdirectory will mechanically solve this, but then you’ll need to optimize the linking structure to circulate PageRank effectively.

• Favor the subdirectory for any microsite linked to the main content (blog, resources, events)
• Reserve the subdomain for functionally distinct content (forum, support, separate web app)
• Plan your 301 redirects by mapping each subdomain URL to its subdirectory equivalent
• Clean up internal linking before migration to avoid redirect chains
• Update sitemap, canonicals, hreflang, and robots.txt after migration
• Monitor Search Console and Analytics for 6-8 weeks post-migration to detect any anomalies