Follow an alias to the name that holds the address, and catch the ones that point nowhere.
Example
CNAME records
As dig shows it
Answer
Findings
Capabilities and processing
Enter a name or paste CNAME records (dig or zone file lines). A name is sent to our server, which asks a public resolver; pasted records are read in your browser.
The whole chain from a name to the record that holds addresses, with the TTL of each step. A target that does not exist is flagged as a dangling alias, the cause of subdomain takeovers, and a CNAME at the zone apex is flagged as invalid.
Example workflow
The sample status page sits behind three aliases. Break it shows a dangling alias and a CNAME at the apex.
Limits and interpretation
A long chain still works, but costs a lookup per step. Nothing is stored.