SnoopTool
Domains and DNS

What is a subdomain?

blog.example.com and example.com/blog look almost identical in a browser bar and behave nothing alike underneath.

A subdomain is a label placed in front of a registered domain name - blog.example.com and shop.example.com are both subdomains of example.com. Each subdomain gets its own DNS records (its own A, CNAME, MX and so on), completely independent of the domain’s own records, which means a subdomain can point at a different server, a different provider, or even a different country than the main site. That independence is the entire point: it lets one registered domain host many separately-configured services under one brand name.

Worked out 2026-09-18 (IST) · standard DNS delegation as specified in RFC 1034

How a subdomain is actually created

Nothing needs to happen at the registrar. Inside the DNS zone for a domain you already control, you add one record whose name is the subdomain label:

Typical subdomain records
NameTypePoints toCommon use
blogCNAMEhosting-platform.example.netA blog on a third-party platform
shopA203.0.113.20A store on its own server
mailMX targetmail.example.comThe mail server itself
apiCNAMEload-balancer.cloudprovider.comA backend service
*A203.0.113.20Wildcard - catches any undefined subdomain

Subdomain vs subdirectory, concretely

Where the two diverge
Subdomain (blog.example.com)Subdirectory (example.com/blog)
Controlled byDNS recordsThe web server’s own routing
Can run on different hostingYes, triviallyNo - same server as everything else
Needs its own SSL certificateYes, unless a wildcard cert covers itNo - covered by the main domain’s certificate
Typical SEO treatmentSometimes evaluated closer to a separate siteGenerally treated as part of the main domain’s authority

When a subdomain is the wrong choice

Splitting a marketing blog onto blog.example.com is common and mostly harmless. Splitting core product surface area - docs, help, pricing - onto subdomains purely for convenience of hosting is the more frequent mistake, because it can dilute the signal search engines associate with the main domain. If the content is not actually served by different infrastructure, a subdirectory is usually the simpler and safer default.

A subdomain’s own records can be inspected the same way as the parent domain’s - see how to check DNS records for a domain.

Sources: IETF RFC 1034 and RFC 1035 (domain names), RFC 2181 (clarifications to the DNS specification), RFC 5321 (SMTP) and RFC 7505 (null MX).

Check your own numbers

See every subdomain a domain currently publishes DNS records for.

DNS LookupA, AAAA, MX, NS, TXT, CNAME and SOA records, live from the resolver.

Frequently asked

Do I have to pay extra or register a subdomain separately?

No. A subdomain is not a separate registration - it is just a DNS record added under a domain you already own, created free in your DNS provider’s control panel. You can create as many as your provider allows.

What is the difference between a subdomain and a subdirectory?

A subdomain (blog.example.com) is a separate DNS name that can point anywhere and run on entirely different infrastructure. A subdirectory (example.com/blog) is a path on the same server as the rest of the site, controlled by the web server’s routing, not by DNS. For SEO purposes a subdirectory generally keeps more of the ranking signal on the main domain; a subdomain is sometimes treated more like a separate site.

What is a wildcard subdomain?

A DNS record of the form *.example.com, which answers for any subdomain that has no record of its own - so random.example.com and anything.example.com resolve without each one being created individually. It is common on platforms that give every customer their own subdomain automatically.

Can a subdomain have its own subdomain?

Yes - shop.eu.example.com is a valid three-level name, and there is no hard limit on depth other than the 253-character overall limit on a fully-qualified domain name.

Related answers

How do I find out who owns a domain?Run a WHOIS or RDAP lookup — but expect the owner’s name to be redacted.Why does WHOIS say “Redacted for Privacy”?GDPR. Since May 2018 registrars publish the operational fields and hide the personal ones.What is RDAP, and how is it different from WHOIS?RDAP is the structured, authenticated replacement for WHOIS. Since 2025 it is the required one.What do domain status codes like clientTransferProhibited mean?They are EPP status codes — the locks and states a domain can be in.

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