Running multiple domains and subdomains on one account
A Measurebase domain subscription is really a root domain plus a subdomain you choose for the tagging server itself — the default suggestion is mbase, e.g. mbase.acme.nl, but you can pick anything. Once you understand that, adding a second property, a subsidiary brand, or a separate GTM container for the same site is just a matter of adding another subdomain.
Your own domain, or a Measurebase-generated one
When you add a domain, you choose between two paths. Use my own domain is the default and the one we recommend — you point a DNS record you control at Measurebase, and you get the full first-party tagging benefits: better cookie lifetime, less ad-blocker interference. Use a Measurebase subdomain skips DNS entirely — a subdomain is generated for you automatically — but since it isn't on your own domain, you lose those same first-party advantages. It's there for quick testing, or for the rare case where you genuinely can't set up DNS, not as a long-term substitute for your own domain.
The DNS record
For your own domain, domain settings shows one A record to add. An A record makes the tagging subdomain genuinely first-party: Safari's tracking prevention detects subdomains that alias a third-party service via CNAME and caps their cookies at 7 days, and an A record avoids that classification entirely — so measurement cookies keep their full lifetime.
Add the record, then use Verify DNS to check it's resolved — SSL is issued automatically once it has, no separate certificate step required.
Three common setups, worked through
Almost every "how should I structure this?" question turns out to be one of three situations. Here's what each looks like in practice.
Multiple domains: a multilingual site
Say your site lives on acme.nl and acme.de. Each root domain becomes its own domain subscription with its own tagging subdomain (mbase.acme.nl and mbase.acme.de), so cookies stay first-party on every country site. Two domains means you'll want at least the Growth plan, which covers 3.
If your languages live on one domain instead (acme.com/nl/, acme.com/de/), you only need a single domain subscription: the tagging subdomain covers the whole root domain, language paths included.
Multiple GTM setups on one domain
If you need a separate property, a subsidiary brand, or just a second, independent GTM container on a domain you've already added, create a new domain subscription for the same root domain and give it a different subdomain, say mbase2.acme.nl next to mbase.acme.nl. Each subdomain runs its own, completely independent tagging server; nothing about the first one changes. Note that each subscription counts toward your plan's domain cap, even on the same root domain.
Development and staging environments
Pointing your staging site at your production tagging server works, but every test click lands in your production container and your real numbers. The clean setup is a separate domain subscription for the staging environment, with its own tagging subdomain that's first-party to wherever staging actually lives: mbase.staging.acme.nl when staging sits on a subdomain (a subdomain of a subdomain is perfectly valid DNS; just enter staging.acme.nl as the domain), or mbase.acme-staging.dev when it's on a separate domain entirely. It sends hits to its own test GTM container, so nothing your team does on staging can touch production data.
A staging environment shouldn't force you into a bigger plan just for the extra slot, though: send us an email and we'll set a custom domain quota on your account for it.
How many domains can you add?
That depends on your plan: the Free and Solo plans cover 1 domain, Growth includes 3, Scale 5 and Business 10. Anything beyond 10 domains is an Enterprise conversation. If you're at your plan's limit, adding another domain prompts you to upgrade rather than silently failing — the same limit is enforced on the backend too, not just as a dashboard nicety, so it's consistent everywhere you might try to add one.