DNS problems rarely announce themselves as DNS problems. A user cannot reach a file share, mail from one domain stops arriving, a site that was migrated last night still resolves to the old host. All of it traces back to a record that is wrong, cached, or not propagated yet.
The tools below answer those questions from the browser, against public resolvers. That matters: they show what the outside world sees, not what your internal DNS server thinks. The gap between the two is usually the whole answer.
Tools in this category
- DNS Lookup Tool — query A, AAAA, MX, TXT, NS and CNAME records for any domain and read the raw answer.
- DNS propagation checker — check the same record against resolvers in different regions after a change, to see who still holds the old value.
- Reverse DNS Lookup — resolve an IP back to its PTR record, the check mail servers run before they accept your message.
- WHOIS lookup — registrar, creation and expiry dates, and the authoritative name servers for a domain.
- SPF record validator — parse an SPF record and count its DNS lookups, so you catch the ten-lookup limit before receivers do.
- DMARC record validator — read a DMARC policy and confirm the alignment and reporting settings are the ones you intended.
How these fit a real investigation
A mail delivery failure is the clearest example. Start with the DNS Lookup Tool to confirm the MX records point where you expect. Run the SPF record validator to check the sending host is authorised and the record is still under the ten-lookup limit. Then read the DMARC policy to see whether a failure means quarantine or outright rejection. If the sending server is your own, finish with a reverse lookup: plenty of receivers drop mail from an IP with no PTR record.
After a migration the order changes. Confirm the new value with the DNS Lookup Tool, then use the propagation checker to find out how much of the world has picked it up. Nothing is broken while TTLs are still expiring, and knowing that saves an afternoon of rollback discussions.
Related guides
- nslookup in Windows: DNS troubleshooting from basic queries to AD diagnostics — the command-line equivalent of the lookup tool, including AD-specific record checks.
- DCDiag: how to diagnose and fix Active Directory problems — most AD replication failures turn out to be DNS failures.
- ipconfig command in Windows: beyond /all — reading and flushing the local resolver cache when a client disagrees with public DNS.
- netsh command in Windows — inspecting and changing DNS client settings from the command line.
Other tool categories
- Network tools — subnet maths, port checks and connectivity diagnostics.
- Security tools — password generation and hashing.
- System tools — Windows command builders and log analysis.
- Data utilities — JSON, JWT, timestamps and cURL conversion.
- Encoding tools — Base64 and URL encoding.
- PowerShell and PowerCLI tools — vSphere command building and PowerShell guides.