Network Tools
DNS Checker
Look up A, AAAA, CNAME, MX, TXT and NS records for any domain.
DNS lookup
This tool is in development. The lookup interface is disabled until its resolver backend is deployed. The reference material below is complete and useful today.
What is DNS?
The Domain Name System translates names people can remember into the addresses machines actually use. When you type a domain, your device asks a resolver, which walks down from the root servers to the top-level domain servers to the domain's own authoritative nameservers, and returns the answer. All of it normally completes in well under a tenth of a second.
The record types that matter
Maps a hostname to an IPv4 address. The most common record type and the one that makes a website reachable.
The IPv6 equivalent of an A record. Its presence is what makes a domain reachable over IPv6.
Points one name at another name rather than an address. Used for subdomains that should follow whatever a provider’s hostname resolves to.
Names the mail servers that accept email for the domain, in preference order.
Holds arbitrary text. In practice it carries SPF, DKIM and DMARC email-authentication policies and domain-ownership proofs.
Declares which nameservers are authoritative for the zone. Changing these delegates the domain to a different DNS provider.
Understanding TTL and propagation
Every record carries a TTL — the number of seconds a resolver may cache the answer before asking again. "DNS propagation" is really just those caches expiring at different times around the world, which is why a change appears instantly for some visitors and hours later for others.
To make a migration quick, lower the TTL to a few minutes at least one full old-TTL period before the change, switch the record, confirm it, then raise the TTL again. Long TTLs are good for stability and performance; short TTLs are good for flexibility.
Common DNS problems
- Missing AAAA record. A domain with only an A record is invisible to IPv6-only clients. Check your own connectivity with the IPv6 checker.
- CNAME at the domain root. Not allowed by the specification. Providers offer ALIAS or ANAME records to work around it.
- Broken SPF or DKIM. A TXT record with a typo will send legitimate mail to spam. Both are strict about syntax.
- Stale NS records. After changing DNS provider, the old nameservers may keep answering until every cached delegation expires.
How this tool will be built
A public DNS lookup service must not become an open resolver that anyone can point at
anything. When the interactive version ships it will accept only the record types listed above
— never
ANY or zone transfers — validate the domain before querying, use a fixed resolver that
the visitor cannot influence, apply per-address rate limits, and cache answers according to their
TTL.
That design is already written down and the validation layer is implemented and tested. What remains is choosing the resolver for the deployment target, which is why the interface above is disabled rather than half-working.
Frequently asked questions
What is a DNS record?
A DNS record is an entry in a domain’s zone that tells the internet something about that domain — which server hosts its website, where its email should go, or which nameservers are authoritative for it. Records are published by the domain owner and cached by resolvers worldwide.
What is the difference between an A record and a CNAME?
An A record points a name directly at an IPv4 address. A CNAME points a name at another name, and the resolver then looks that one up in turn. A CNAME cannot coexist with other records on the same name, which is why it cannot be used at the root of a domain.
Why do DNS changes take time to appear?
Because of TTL caching. Every record carries a time-to-live telling resolvers how long they may reuse the answer. Until that expires, resolvers keep serving the old value. Lowering the TTL a day before a planned change is the standard way to make a migration fast.
What is an MX record?
An MX record specifies which mail servers accept email for a domain, each with a preference number. Lower numbers are tried first, and equal numbers share load. A domain with no MX record cannot reliably receive email.