What is SSLurp?

SSLurp is a certificate checking tool that connects directly to IP addresses to retrieve and inspect SSL/TLS certificates. It was built to solve a simple problem: sometimes you need to see exactly what certificate a specific server is presenting, without DNS resolution getting in the way.

Whether you're testing a new certificate before updating DNS, troubleshooting a CDN configuration, or just curious what a particular IP is serving, SSLurp gives you the answer.

The Story Behind It

SSLurp started as a weekend experiment — a collaborative build between Ian McCutcheon and Claude, Anthropic's AI assistant. The goal was simple: see if we could ship something useful, end to end, in a short timeframe.

The full story of how it came together is documented on the Workshop:

Related Reading

If you're interested in certificates and DNS security, these articles from the Workshop might be useful:

• Wildcard Certificates - The Misunderstood Shortcut
• Taking Back Control: CAA Records

Technical Stack

SSLurp is intentionally simple:

• Runtime: Bun
• Framework: Hono
• Certificate Retrieval: Native TLS sockets with OpenSSL fallback for chain retrieval

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