Subdomains vs Subdirectories SEO Guide - Blogging Flail

The subdomain versus subdirectory argument has outlived almost every other SEO debate of its era, and it survives because both camps can point at real data. This article is a good example of the pro subfolder case, and it is worth reading alongside a clear account of what its evidence can and cannot support.

What the source actually tested

The author ran a test on Vircara, a domain that had been established for over three years at the time. A blog had been set up on the subdomain blog.vircara.com in March 2012, with links built to it. The target phrase was choosing a career, and on the subdomain the page ranked outside the top 100 and did not surface in Google Blog search either.

The content was then moved to the subdirectory vircara.com/blog/. Within two weeks the page was reported at position 57. The author revisited the piece in mid 2015 and again in July 2021, maintaining the conclusion that subdirectories inherit the parent domain's accumulated authority in a way subdomains do not.

The recommendations that follow from it are sensible enough on their own terms: use subdirectories for a blog attached to an established domain and for content meant to benefit from existing authority, and reserve subdomains for multi language content targeting different markets, franchise specific regional pages, and genuinely separate product lines.

Reading the evidence honestly

The problem is not that the observation is false. The problem is that one page moving from unranked to position 57 is compatible with several explanations, and the hostname is only one of them.

None of these rule out a hostname effect. They mean this test cannot distinguish a hostname effect from four other things.

What Google says

Google's search relations team has been consistent for years: subdomains and subdirectories are treated equivalently in search, and the decision should be made on operational grounds. In a September 2021 office hours session John Mueller put it plainly, saying that from Google's point of view it does not matter, while adding the useful qualifier that related content should be grouped together on the same site as much as possible and that a subdomain makes sense when it has something genuinely different to offer.

The second half of that is the part people skip, and it is where the two positions actually converge. Google is not saying build your blog wherever you like with no consequences. It is saying the hostname string is not itself the mechanism. Grouping related content together tends to win because of internal linking, crawl consolidation and topical coherence, all of which a subdirectory makes easy and a subdomain makes easy to neglect.

The differences that are unambiguously real

Set the ranking question aside and there is a concrete list of things that genuinely change when you pick one over the other. These are the ones to decide on.

Rows one to four favour the subdirectory. Rows five to seven are the legitimate reasons teams choose a subdomain and are engineering constraints, not SEO ones.

Doing the migration properly if you decide to move

The mechanics are the same as any hostname migration. The failure mode that costs the most is a blanket redirect: sending every old post URL to the new blog index rather than to its own new URL. That converts a clean signal transfer into a mass soft 404 event.

# nginx: one to one map, not a blanket redirect
location ^~ /blog/ {
  proxy_pass http://blog_backend/;
  proxy_set_header Host $host;
}

# On the legacy host, preserve the path
server {
  server_name blog.example.com;
  return 301 https://example.com/blog$request_uri;
}

Then verify, rather than assume, that the map is one to one. Take the full legacy URL list from your last crawl and confirm each entry resolves in a single hop to a live page.

while read u; do
  out=$(curl -s -o /dev/null -w '%{num_redirects} %{http_code} %{url_effective}' -L "$u")
  set -- $out
  if [ "$1" != "1" ] || [ "$2" != "200" ] || [ "$3" = "https://example.com/blog/" ]; then
    echo "REVIEW $u -> $out"
  fi
done < legacy_blog_urls.txt

The third clause in that condition is the important one. It catches the case where everything technically returns 200 but every legacy post has been funnelled into the blog index, which is the exact failure the redirect was supposed to prevent.

What's changed since

The article was written in 2014 and last revisited by its author in July 2021, and the landscape has shifted underneath it in two ways. First, the PageRank sculpting practice that made subdomain blogs perform badly in the early 2010s, nofollowing internal links to conserve equity, has been obsolete since Google changed how nofollow is handled, so the mechanism that produced many of the original subfolder wins simply is not there any more. Second, edge platforms have made path based routing far cheaper than it was: reverse proxying a separately hosted application into a path on the main hostname is now a configuration file rather than an infrastructure project, which removes most of the historical engineering argument for the subdomain.

The net effect is that the practical recommendation has converged on the article's conclusion even though its reasoning does not hold. Put the blog in a subdirectory, not because the hostname is a ranking factor, but because doing so makes internal linking, reporting and crawl management easier, and because the cost of doing it has fallen to near zero.

Related reading on this site

For a longer treatment of the architectural question, see how a subdomain strategy can harm your SEO. The HotPads blog migration is the most famous example of exactly this confound being publicly picked apart, and the robots.txt reference covers the per hostname scoping rule that catches out most subdomain owners.

FAQ

Source: http://www.bloggingflail.com/subdomains-vs-subdirectories-seo/