Subdomains explained, from shop. to book. and more

A subdomain is a word added in front of your domain, like book.yourdomain.com or shop.yourdomain.com, that can point somewhere completely different from your main website. You create it for free in your domain's DNS settings, and it lets a booking system, an online store or a customer portal appear under your own name instead of the software company's. It is useful when a separate service runs part of your business. It is unnecessary when all you want is another page on your existing site.

The parts of a web address

Take book.oakridgevet.com:

com is the ending.
oakridgevet is the name you registered. Together, oakridgevet.com is your domain, and you pay a yearly fee for it.
book is the subdomain. You did not buy it separately; any word you choose in front of your domain is yours to create.

You already use one subdomain without thinking about it: www. www.oakridgevet.com is technically a subdomain of oakridgevet.com. Most sites simply set www to show the same website as the bare domain.

Compare that with oakridgevet.com/book, which is a page on your main website. Same idea for a visitor, very different behind the scenes. A page lives inside your website. A subdomain can be a whole separate system run by someone else.

How a subdomain gets pointed somewhere

In your DNS settings (the list of records that tells the internet where your website and email live), you add one record for the subdomain:

A CNAME record is the usual choice. It says "book.oakridgevet.com is really this other name", for example a name the booking company gives you. The company keeps its servers running and you never need to update the record if they move.
An A record points the subdomain at a numbered server address. It is used when a service gives you an IP address instead of a name.

Then you tell the service, in its settings, that you want to use book.oakridgevet.com. It checks the record, issues a security certificate so the address works with https, and starts answering visitors there. The details vary; the service's help pages list the exact record to add.

Common uses for small businesses

shop. An online store on Shopify, Square Online, BigCommerce or similar, while the main website stays where it is. Putting your online store on a subdomain covers that setup in detail.
book. or appointments. A scheduling tool for a salon, clinic, tutor or contractor.
portal. or clients. A client login for an accountant, insurance agent or property manager, often provided by their practice software.
pay. or invoices. A billing page from invoicing software.
order. Online ordering for a restaurant, usually from the ordering company.
careers. A job board from a hiring tool.
mail. or webmail. A shortcut to your email login, set up by your email provider.

Each of these lets the software do its job while customers still see your name in the address bar, which feels more trustworthy than being sent to some-booking-company.com/oakridge-vet-12345.

When a subdomain is the wrong tool

For a blog, a menu, a gallery or a services page. Put these on your main site as normal pages. A subdomain is treated more like a separate website by search engines, so splitting your content across them does not help your main site get read as one whole.
For each town or service. plumbing.yourdomain.com and drains.yourdomain.com just make your business look scattered. Use pages.
As a way to save money on a second domain. If you want a different brand, buy a separate domain.

Subdomains and email

Subdomains rarely appear in email addresses for small businesses. Your addresses stay [email protected]. Some newsletter and invoicing tools do ask you to set up a subdomain such as mail. or em. for sending; that keeps their sending reputation separate from your everyday mail and is fine to do. The tool gives you the records.

Adding or changing a subdomain does not touch your main domain's email records, as long as you edit only the subdomain's own line. MX records and why changing your website can break email explains which lines belong to email.

The cleanup most owners forget

When you stop using a service, remove its subdomain record from your DNS. A CNAME that still points at a cancelled store or booking account is called a dangling record. In some cases a stranger can sign up with that same service, claim your subdomain, and put their own page at shop.yourdomain.com, under your name. Deleting the record when you cancel closes that door.

Do a quick review once a year:

Open your DNS settings and list every subdomain record.
For each one, type the address into your browser.
If it shows an error, a "store not found" page, or something you do not recognize, and you no longer use the service, delete the record.

Things to check when you add one

Make it short and obvious. book. beats onlineappointmentscheduling. Customers may type it.
Link to it from your main site, in the menu and on the relevant page, so people find it without typing.
Link back. Most booking and store tools let you set a "back to website" link. Point it at your home page.
Match the look. Add your logo and colors in the service's settings so the jump between sites does not feel like leaving your business.
Test on a phone, with https, after the service says the setup is complete.

Quick summary

A subdomain is a free prefix on your domain that can point at any service.
Use one for separate software: a store, bookings, a client portal.
Use normal pages for normal content.
Remove subdomain records for services you cancel.

If your main website is the part that needs fixing before you add a booking or store subdomain beside it, you can see your site rebuilt first, with a clear button that links to your booking or store address.