Domain Diagnostics is part of DevStudio — a free, in-browser collection of developer utilities that work without sign-up, installation, or any backend service. WHOIS, domain-expiry warning and DNSBL / RBL multi-list lookup, all running entirely on your device. Because the page never uploads what you paste, you can run sensitive payloads, configuration files, secrets, or production data through it with confidence: nothing leaves your browser tab. Use Domain Diagnostics for ad-hoc debugging, code review, log triage, release prep, learning a new format, or as a quick scratchpad while you build. If you use this tool a lot, pair it with DNS Toolkit, Mail Diagnostics, Web Probes, and the rest of the DevStudio toolkit for related developer workflows.