Running multiple domains and subdomains on one account
A Measurebase domain is your main domain plus a tagging subdomain you choose on it · the default suggestion is mbase, e.g. mbase.acme.nl, but you can pick anything. You always enter the main domain itself, such as acme.nl: a leading www. is stripped, and Measurebase checks straight away that the domain is real and has a DNS zone. 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 the same main domain again with another tagging subdomain.
The DNS record
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. Safari also caps cookies from a subdomain that runs on a different server than your website; Same-Origin Tracking solves that by serving your tagging from your own domain.
Add the record, then use Verify DNS now 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 main domain is added as its own domain, 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: the tagging subdomain covers the whole main 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, add the same main domain again as a new domain subscription and give it a different tagging subdomain, say mbase2.acme.nl next to mbase.acme.nl. Each setup is completely independent; nothing about the first one changes. Note that each subscription counts toward your plan's domain cap, even on the same main 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. When staging sits on a subdomain such as staging.acme.nl, you still enter the main domain acme.nl and give the setup a tagging subdomain of its own, such as mbase-staging.acme.nl. When staging runs on a separate domain entirely, you enter that domain and use, say, mbase.acme-staging.dev. 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.