Every SSL/TLS certificate ever issued for this name, indexed from public CT logs.
# Python
$ pip install ct-radar
$ ct-radar duolingo.com | httpx -silent# Go
$ go install github.com/imfht/ct-radar-cli/cli@latest
$ ct-radar duolingo.com | nucleiThis page lists every X.509 (SSL/TLS) certificate ever issued for duolingo.com and its subdomains, as recorded in public Certificate Transparency (CT) logs. CT logs are an immutable, append-only record of every certificate issued by participating Certificate Authorities (CAs), as required by the major browsers since 2018.
Subdomain enumeration via CT logs is one of the highest-signal techniques in reconnaissance — every time a TLS certificate is issued, all Subject Alternative Names (SANs) on that certificate become public. Internal and forgotten subdomains regularly show up here days after they're set up.
To monitor duolingo.com for newly-issued certificates in real-time (useful for detecting unauthorized issuance, phishing variants, or shadow IT) add it to your watchlist (Pro plan).