You are adding a blog, an online shop, a help centre or a customer portal to your website. Should it live at blog.example.com or at example.com/blog? The subdomain vs subdirectory decision affects how the section is hosted, how cookies and security work, and how search engines see your site. Neither option is always better; each fits different situations. This article helps you choose based on how your site is actually built.
What the difference is
A subdomain is a separate host name under your domain, such as shop.example.com. It has its own DNS record, so it can point at a completely different server or platform from your main site.
A subdirectory (or subfolder) is a path on the same host, such as example.com/shop. Requests reach the same server as your main site, which then decides how to handle the path, either serving the content itself or forwarding the request to another application behind the scenes.
Subdomain: https://help.example.com/articles/reset-password
Subdirectory: https://example.com/help/articles/reset-passwordHow they compare
| Factor | Subdomain | Subdirectory |
|---|---|---|
| Setup | One DNS record (often a CNAME to a platform) | Same server, or a reverse proxy rule |
| Can run on separate hosting or a SaaS tool | Easily | Only with a reverse proxy |
| SSL certificate | Needs its own, or a wildcard | Covered by the main site's certificate |
| Cookies | Isolated by default | Shared with the main site |
| Search engines | May be treated more like a separate site | Clearly part of the main site |
| Analytics | Needs cross-domain configuration in some tools | Works out of the box |
| Failure isolation | An outage on one does not affect the other | Shares the main site's server and fate |
The SEO question
This is usually why people ask. Google has said publicly that its systems can handle both structures and that you should pick whatever is easiest for you to maintain. In practice, a subdirectory makes it unambiguous that the content belongs to your main site, and links to your blog articles clearly support the same host name as your product pages. Content on a subdomain can still rank well, but search engines may evaluate it more independently, and you have a second property to set up in tools such as Search Console.
Many marketing teams therefore prefer subdirectories for content that is meant to build the main site's visibility: blogs, guides, resource libraries and landing pages. Be wary of anyone who promises a specific ranking change from moving between the two; the content itself matters far more than its URL structure.
The technical and security questions
Hosting and platforms
Many SaaS tools, including helpdesks, status pages, booking systems and some shop platforms, only support custom domains as subdomains. You create a CNAME and they handle hosting and certificates. Serving them under a subdirectory instead requires a reverse proxy (for example an Nginx location block or a CDN rule) that forwards /help/ to the provider, and the provider has to support being served that way. That adds moving parts you will need to maintain.
Cookies and isolation
Browsers scope cookies by host. A subdirectory shares cookies and the same origin with your main site, which is convenient when both are one application but risky when they are not. If your blog runs a CMS with many plugins and your customer portal handles payments, putting them on the same origin means a vulnerability in the blog could expose the portal's session. Separate subdomains give each application its own origin, which browsers keep apart for scripts and storage. Avoid setting cookies with Domain=example.com unless you really mean every subdomain to receive them.
Certificates
Each subdomain needs to be covered by a certificate, either its own or a wildcard (*.example.com). Platforms often issue these automatically. Use the SSL checker after setup to confirm each host name has a valid certificate.
Practical recommendations
- Blog, guides, marketing content: subdirectory, if your main site's platform can host it or you can proxy it cleanly.
- Web application or customer portal (
app.example.com,portal.example.com): subdomain, for isolation, independent deployment and scaling. - Third-party SaaS (help desk, status page, careers site): subdomain, because that is what the provider supports.
- Language or regional versions: either works; subdirectories such as
/en/and/de/are simplest to manage on one platform, combined withhreflangtags. - Staging or test sites: subdomain, protected by a password and excluded from search engines.
Setting each one up
For a subdomain, add a record in your DNS zone, such as help CNAME yourcompany.helpdesk-provider.com., or an A record to your own server. You can confirm it resolves with a DNS lookup. For a subdirectory served by another application, configure your web server or CDN to proxy the path, for example in Nginx:
location /blog/ {
proxy_pass http://127.0.0.1:8080/;
proxy_set_header Host $host;
proxy_set_header X-Forwarded-Proto $scheme;
}The application behind the proxy must also be told its public base URL, or it will generate links and redirects without the /blog prefix.
Changing your mind later
Moving content between a subdomain and a subdirectory is possible, but treat it as a migration: map every old URL to its new one, use permanent (301) redirects, update internal links and sitemaps, and expect some search fluctuation while things settle. Choosing carefully up front is cheaper.
Key takeaways
- Subdomains are separate host names that can live anywhere; subdirectories are paths on the main site.
- Subdirectories keep content clearly part of the main site and are popular for blogs and marketing pages.
- Subdomains suit applications, SaaS tools and anything that benefits from security or hosting isolation.
- Pick the structure you can maintain well; content quality matters more for search than URL shape.