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DNS Lookup

Simon Willison's Blog / 3/23/2026

💬 OpinionDeveloper Stack & InfrastructureTools & Practical Usage
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Key Points

  • The post highlights a practical discovery that Cloudflare’s 1.1.1.1 DNS service (and 1.1.1.2 / 1.1.1.3) provides a CORS-enabled JSON API.
  • The author uses that capability to run DNS queries from a browser-friendly interface against the three resolvers.
  • Claude Code was used to build a UI for executing DNS lookups for malware-blocking and malware+adult-content filtering variants.
  • The entry is presented as a “TIL” beat, pointing readers to the “DNS Lookup” tool at tools.simonwillison.net.
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22nd March 2026

Tool DNS Lookup

TIL that Cloudflare's 1.1.1.1 DNS service (and 1.1.1.2 and 1.1.1.3, which block malware and malware + adult content respectively) has a CORS-enabled JSON API, so I had Claude Code build me a UI for running DNS queries against all three of those resolvers.

Posted 22nd March 2026 at 7:16 pm

This is a beat by Simon Willison, posted on 22nd March 2026.

dns 32 cors 26 cloudflare 30

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