Why this tool needs a server at all

Browsers deliberately don't expose raw DNS resolution to JavaScript — there's no `dns.resolve()` available to a web page, for the same sandboxing reasons a page can't open an arbitrary TCP socket. Getting an actual answer from the DNS system means sending the query from somewhere that can make one, which is why this tool (and the others grouped under "Network Diagnostics") is one of the few on this site that involves this site's own backend: the hostname you enter is sent to the server, which performs the resolution and returns the result.

Every server-assisted tool discloses this on its own page — the full data-handling breakdown is in the privacy policy.

The record types, briefly

• A / AAAA — the IPv4 / IPv6 address(es) a hostname points to. This is the record most things need to actually connect to a host.
• CNAME — an alias pointing to another hostname, which is then itself resolved. A domain can't have a CNAME alongside other record types at the same name (a common source of "why won't this record save" DNS panel errors).
• MX — the mail server(s) responsible for accepting email for the domain, each with a priority (lower number = tried first).
• TXT — free-form text, widely reused for domain verification codes and, notably, SPF policy strings (see this site's dedicated SPF/DKIM/DMARC tools for a parsed view of those).
• NS — the authoritative name servers for the domain or subdomain.
• SOA — one record per zone holding administrative metadata: the primary name server, an admin contact, and timing values (refresh/retry/expire/minimum-TTL) used by secondary name servers.
• PTR — the reverse mapping from an IP address back to a hostname, looked up via the special in-addr.arpa (IPv4) or ip6.arpa (IPv6) zone — this is why a PTR lookup takes an IP as input rather than a hostname.

Reading a "no data" result correctly

A domain having zero records of the type you asked for (e.g. no AAAA record because it isn't IPv6-enabled) is a completely normal, valid DNS answer, not a failure — it just means that record type was never published. This is different from the domain not existing in DNS at all, which is a distinct error condition. This tool passes through the underlying resolver's error message specifically so you can tell those two cases apart rather than guessing from a generic "lookup failed."