DNS

Subdomain Finder

Discover subdomains via Certificate Transparency logs. Passive enumeration — no brute force.

Uses Certificate Transparency (crt.sh). Passive scan — no DNS brute force.

How to use

  1. Enter a domain, URL, or value relevant to Subdomain Finder.
  2. Run the check and review the output carefully.
  3. Apply recommended fixes, then run the check again to verify.

Common use cases

  • Pre-deployment validation for Subdomain Finder.
  • Incident triage when security checks fail in production.
  • Periodic security review as part of technical SEO and hardening.

Example inputs

example.comgoogle.comgithub.com

Common issues and fixes

No subdomains found

Domain may have no SSL certs in CT logs, or subdomains use wildcard only. Try a larger domain.

crt.sh timeout

Certificate Transparency service can be slow for popular domains. Retry after a few seconds.

Recommended remediation

Uses crt.sh — passive OSINT. No brute force or DNS enumeration. Combine with DNS lookup for IP resolution.

FAQ

Is Subdomain Finder free to use?

Yes. This tool is free and can be used without account registration.

Do you store submitted values?

Only the minimum processing needed for the check. For client-side tools, data stays in your browser.

How should I use these results?

Use the output as a diagnostic baseline, apply fixes in your stack, then re-run the check to confirm remediation.

Related security tools

SSL Checker

Verify SSL/TLS certificate details, issuer, expiry date, and certificate chain for any domain.

DNS Lookup

Query DNS records (A, AAAA, MX, TXT, NS, CNAME) for any domain using public DNS API.

WHOIS Lookup

Retrieve domain registration details including registrar, registrant, creation date, and expiry.

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