The SOA record marks the Start of Authority for a zone. Every zone has exactly one, and it defines the zone's administrative parameters.
The Start of Authority record holds the master settings for your DNS zone: the primary name server, the responsible party's email (written with a dot instead of an @), and a serial number that increments every time you edit the zone. Secondary name servers compare serial numbers to decide when to pull a fresh copy, so a serial that fails to advance is a classic cause of stale replicas that never pick up your changes.
The SOA also carries the refresh, retry, expire, and minimum timers that control how secondary servers sync and how long negative (NXDOMAIN) answers may be cached. Reading these values tells you a lot about how your provider runs the zone and how quickly deletions will disappear from resolvers. This checker retrieves the SOA from multiple locations so you can confirm every resolver agrees on the same serial and primary server. A mismatched serial across regions usually means a recent edit is still propagating between your provider's own name servers, and you should wait before troubleshooting further.
Frequently asked questions
- What is the SOA serial number for?
- It versions the zone. Secondary servers refresh when the serial increases, so it must advance on every change.
- How many SOA records can a zone have?
- Exactly one, always at the zone apex.