CNAME Lookup
See what a hostname is an alias for.
A CNAME record makes one hostname an alias for another. Looking up www.example.com might return example.com, and the resolver then starts again on that name to find an address. It is the mechanism behind nearly every "add a CNAME pointing at us" instruction from a CDN, SaaS platform or email provider.
Two rules cause most CNAME confusion. First, a name with a CNAME may hold no other records — so you cannot put a CNAME on a domain that also needs MX or TXT records, which is why the apex of a domain cannot be a CNAME and providers offer ALIAS or ANAME records as a proprietary workaround. Second, CNAMEs chain: an alias can point at another alias, and each hop is another round trip before anything resolves.
The security dimension is worth understanding. If a subdomain CNAMEs to a cloud resource that is later deleted, the alias keeps pointing at a hostname nobody owns — and on many platforms anyone can claim that name and serve content from your subdomain. This is subdomain takeover, and the vulnerable state is exactly a CNAME whose target does not resolve.
What this tool does
See the real target
A CNAME points at another name, which may itself be an alias. The answer shows what this hostname actually delegates to.
Catch dangling aliases
A CNAME pointing at a de-provisioned SaaS or cloud hostname is the precondition for subdomain takeover. An alias whose target no longer resolves is worth acting on today.
Verify vendor setup
Most SaaS onboarding asks for a CNAME. This confirms yours resolves to the exact hostname the vendor specified, rather than something close to it.
Understand apex limits
A CNAME cannot sit on a bare domain. If a lookup for the apex comes back empty, that is the specification, not a misconfiguration.
Frequently asked questions
What is a CNAME record?
A CNAME ("canonical name") record makes one hostname an alias for another. When a resolver finds a CNAME it restarts the lookup against the target name, following the chain until it reaches records with actual addresses.
Why can I not use a CNAME on my root domain?
Because the DNS specification forbids a CNAME from coexisting with any other record on the same name, and a root domain must carry SOA and NS records. Providers work around this with ALIAS, ANAME or flattened-CNAME features that resolve the target server-side and answer with an address record instead.
What is the difference between a CNAME and a redirect?
They operate at different layers. A CNAME is DNS: the browser resolves a different name but the URL in the address bar never changes. An HTTP redirect is the web server telling the browser to request a different URL, which does change the address bar. If you want visitors to land on a different address, you need the redirect, not the CNAME.
How many CNAMEs can chain together?
There is no hard limit in the specification, but resolvers cap the chain — typically around eight to sixteen hops — and abandon the lookup beyond that. Each hop costs a round trip, so long chains are slow as well as fragile. Keep it to one or two.
What is a dangling CNAME and why does it matter?
A dangling CNAME points at a hostname that no longer resolves, usually because the cloud or SaaS resource behind it was deleted. On platforms that let anyone claim an unused hostname, an attacker can register the target and serve their own content from your subdomain — which means valid TLS, your cookies in scope, and your brand on their page.
Does a CNAME slow down my site?
Slightly, for the first visitor. Each alias hop is an extra DNS lookup before a connection can open, though the results are then cached for the TTL. One hop is negligible; a chain of five on a latency-sensitive path is worth flattening.
Monitor it, don't just check it
One-off checks catch what is broken today. CertNotify watches your certificates, domains, DNS and code continuously and tells you before something breaks.