Overview
Simon Willison discovered that Cloudflare's DNS services have a CORS-enabled JSON API and built a web UI to query DNS records directly from the browser. The tool allows users to run DNS lookups against Cloudflare's standard, malware-blocking, and family-safe DNS resolvers.
Key Points
- Cloudflare's 1.1.1.1, 1.1.1.2, and 1.1.1.3 DNS services offer CORS-enabled JSON APIs - enables DNS queries directly from web browsers without server-side code
- Built a web interface using Claude Code that queries all three Cloudflare DNS resolvers simultaneously - compare results across standard, malware-blocking, and family-safe filtering
- The different resolvers provide varying levels of content filtering (standard, malware blocking, malware + adult content blocking) - users can see how DNS filtering affects domain resolution