domain-infra-history
crt.sh (Cert Transparency)
A queryable window into Certificate Transparency logs, the public record of TLS certificates — which makes it a way to uncover historical certificates and subdomains for a domain. You query it on the website, and the same query can return JSON without a key. Researchers use it to reconstruct a domain's infrastructure history. It is frequently overloaded and errors out under load, so retry if a query fails.
No programmatic check — opens the archive’s own search.
Why it’s useful & how it works
Alive but OVERLOADED (502) — crt.sh is frequently saturated. Keyless cert-transparency/subdomain JSON when up; retry with backoff. Feeds the domain-dig sister project. Niche/link-catalogue tier.
API access
https://crt.sh/?q=%25 .<domain>&output=json (keyless; often overloaded)
Access
Catalogue link only — open the archive to search it yourself.