Subdomain FAQ

Short answers to the questions people ask most often when setting up subdomains. Each answer links to a longer guide where one exists.

What is a subdomain?

A subdomain is a name to the left of your registered domain, such as blog in blog.example.com. You create it in the DNS settings of the domain; no extra registration or fee is needed. Each subdomain can point to a different server or service. See What is a subdomain?

How do I create a subdomain?

Log in to whoever hosts DNS for your domain (often the registrar, Cloudflare or your web host), add a new record with the subdomain as the name, and point it at a server IP (A or AAAA record) or another hostname (CNAME record). Then configure the web server or service to answer for that name and add an SSL certificate. The home page guide walks through each step.

Should I use an A record or a CNAME?

Use an A (IPv4) or AAAA (IPv6) record when you know the server's IP address and control the server. Use a CNAME when a service gives you a hostname to point to, such as a hosted shop, help desk or CDN, because the provider can then change IP addresses without you editing DNS. A name that has a CNAME cannot have other records of its own. More in the DNS record guide.

How long does a new subdomain take to work?

A brand-new record is usually visible within minutes. Changes to an existing record can take as long as the record's previous TTL (time to live) to reach every resolver, which is commonly between five minutes and a day. Lowering the TTL a day before a planned change shortens the wait.

Do I need a separate SSL certificate for each subdomain?

Not necessarily. You can issue a certificate per subdomain (free with Let's Encrypt), list several names on one certificate, or use a wildcard certificate for *.example.com, which covers one level of subdomains. Wildcard certificates from Let's Encrypt require DNS-based validation. See SSL certificates for subdomains.

Are subdomains bad for SEO?

Search engines can rank subdomains well, but they often treat a subdomain more like a separate site than a folder. For a blog or content section, a subfolder (example.com/blog/) is usually the simpler choice; subdomains suit apps, APIs, regional sites and anything on a different platform. The subdomain vs. subfolder guide covers the trade-offs.

What is a wildcard subdomain?

A wildcard DNS record (*.example.com) answers for every subdomain that does not have its own record. It is useful for multi-tenant apps where each customer gets a name, but it also means typos and random names resolve, so the web server should handle unknown names deliberately. See wildcard subdomains.

What is a subdomain takeover?

If a subdomain's CNAME still points to a third-party service (for example a deleted cloud storage bucket or hosted page) after you stopped using it, someone else may be able to claim that resource and serve content on your subdomain. The fix is simple: remove DNS records as soon as you shut down the service they point to, and review your DNS zone regularly. See subdomain security.

Is it legal to look up other people's subdomains?

Looking up public DNS records is normally fine, but actively probing or scanning systems you do not own may break laws or terms of service. Only test domains you own or are authorised to assess.

Does SubDoms offer hosting, monitoring or paid plans?

No. SubDoms is a free informational site. The lookup tools run in your browser using public DNS services, and there are no accounts, subscriptions or paid plans.