DNS checker

Use this after changing DNS to see whether the change has spread, and to confirm who may issue certificates for the domain and whether answers are signed.

Propagation — resolvers can disagree

A DNS change does not reach the world at once. Each resolver keeps its previous answer until that copy expires, then fetches a new one. This check asks Google, Cloudflare, Quad9 and KT separately and shows whether they agree. If they do not, the change is still spreading.

CAA — restrict who can issue certificates

Without a CAA record, any certificate authority in the world may issue a certificate for your domain name. One record limits that to the authorities you name, which narrows the room for mis-issuance.

DNSSEC — signatures against tampering

DNSSEC signs DNS answers so that tampering in transit can be detected. It is not mandatory, but most registrars now enable it with a single switch.

Start with the failing service, not the score

If visitors cannot open the site, check DNS, the certificate and the redirect destination first. If outgoing mail fails, inspect SPF, DKIM and DMARC together. If the site works and only a header is missing, review what that header would change before deploying it. These are different problems and should not be treated as equally urgent.

How to interpret your website check →

Only public information is read (DNS records, certificates, HTTP responses). Nothing is logged in, and no load is placed on the site.

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