Practical guidance
Check A, AAAA and CNAME records for websites, and MX plus relevant TXT records for mail. Comparing recursive and authoritative answers helps distinguish stale caches from zone errors. Use the exact hostname, including subdomains.
Before using this tool
Define what you need from DNS lookup and prepare the relevant input. When diagnosing a live service, record the test time and connection conditions so you can compare results after configuration changes. Check findings against the documentation for your software.
Tool availability
This is currently an information page. No working form, calculations or submission to diagnostic services is available yet. The interface and supported input formats will be documented when functionality is released.