c0deur

• https://scans.io/
• https://commoncrawl.org/
• https://web.archive.org/ (For JS snippets this can be extremely handy. See killbox.sh below that was written for a HackerOne event.)
• https://www.shodan.io/
• https://opendata.rapid7.com/
• https://www.virustotal.com/en/documentation/public-api/ (You can fetch previously-scanned URLs via the API.)
• https://securitytrails.com/
• https://threatcrowd.org/
• https://dnsdumpster.com/
• https://crt.sh/