Search Certificate Transparency logs
Enter a domain and click "Search".
Certificate Transparency logs are public, append-only records of issued TLS certificates. Searching them reveals subdomains, issuers and expiry dates.
What a browser can and cannot do
This page calls crt.sh (Sectigo) first and falls back to Cert Spotter (SSLMate). Both allow cross-origin requests from a browser, but both are free public services: crt.sh is often slow or overloaded on large domains and then answers with a 5xx or times out, and Cert Spotter allows only about 10 unauthenticated requests per hour per IP. Your search term is sent to whichever service answers. If both fail, no result is shown and none is invented. A browser cannot query the CT logs directly: they expose raw RFC 6962 endpoints with no search by name. You can run the same query yourself:
Only certificates logged in CT are listed. Certificates a CA never logged (private CAs, some older certificates) will not appear, and the list says nothing about which hosts are live.