SecurityTrails Alternative for Subdomain Discovery

• Subdomains from three sources, merged and deduplicated: CT logs via crt.sh, HackerTarget and AlienVault OTX. Each result shows which sources answered.
• Live DNS. Up to 200 subdomains are resolved to IP addresses, so you see which names exist today rather than which ever existed.
• Wildcard DNS warning. Random names are resolved first; if they answer, the results are marked as possibly inflated by a wildcard record.
• Takeover risk for the first 20 subdomains: a CNAME lookup plus an HTTP probe that looks for records pointing at unclaimed cloud resources.
• CSV export for your own inventory or a pentest report.

Next steps for the hosts you find: current records in the DNS lookup, registration data in WHOIS, and other sites on the same address in reverse IP.

SecurityTrails, now a Recorded Future company, sells data rather than a checker. Its own pages list capabilities the tool above does not have:

• DNS history. "10+ years of data" for A, AAAA, MX, NS, SOA and TXT records, through the API's history endpoints. We only show what resolves now.
• WHOIS history and reverse WHOIS search, useful for linking domains to one owner.
• Associated domains: other domains linked to the same organization; the API example matches them on a WHOIS email.
• IP and PTR search with its query language; the API page says these DSL queries need the Professional plan or higher.
• Scale. The sign-up page says it updates over 5 billion DNS records daily. A dataset that size finds subdomains that never appeared in a certificate.

For threat hunting, brand-abuse investigations or M&A due diligence, that history is the product, and a free on-demand scan does not replace it.

SecurityTrails' pricing page lists the API at $500/month (Professional, 20,000 queries a month) and $1,500/month (Business, 65,000 queries), with Enterprise on request. It also describes an OSINT Toolkit with 2,500 queries a month for researchers, without a price on that page. A free sign-up form exists, but the free quota is not published on the pricing page.

The tool above is free on the site with a per-minute rate limit. Paid Enterno plans start at $5/month and are about monitoring (uptime, SSL, DNS and alerts), not about buying a data feed. If you need a programmatic subdomain list, the MCP tool check_subdomain_enum works with an API key from a free account.

No single source sees everything, so combine them:

• Certificate Transparency search, for names in issued certificates. See our crt.sh alternative page for direct database access and other CT tools.
• Passive DNS map tools such as DNSdumpster; compared on our DNSdumpster alternatives page.
• Your own zone file. If you control the domain, an export from your DNS provider is the only complete list; compare it with the tool's output to find hosts nobody remembers creating.