SecurityTrails Alternative — Free Subdomain Finder

What is SecurityTrails?

SecurityTrails is a commercial SaaS platform, acquired by Recorded Future, focused on DNS intelligence and historical internet data. Its core differentiator is depth over time: the platform archives every DNS record change observed for millions of domains — A, MX, NS, TXT, CNAME, and more — giving security and intelligence teams a full historical picture of how a domain's infrastructure has evolved. Alongside subdomain enumeration, it offers WHOIS history (who owned a domain and when), IP history (what IPs a hostname has resolved to over the years), and reverse lookups (what domains have ever pointed to a given IP).

The platform is API-first with well-documented endpoints and integrations for Splunk, Cortex XSOAR, and other enterprise security tooling. Pricing is tiered: a free account gets 50 API queries per month — enough to understand the product but not enough for sustained use. Individual paid plans start around $50/month, team plans run higher, and enterprise tiers with SLA commitments go into the thousands monthly.

# SecurityTrails API (requires key)
curl -H "apikey: YOUR_KEY"   "https://api.securitytrails.com/v1/domain/example.com/subdomains"

# Historical DNS for a subdomain
curl -H "apikey: YOUR_KEY"   "https://api.securitytrails.com/v1/history/example.com/dns/a"

# WHOIS history
curl -H "apikey: YOUR_KEY"   "https://api.securitytrails.com/v1/domain/example.com/whois"

Feature comparison

Where SecurityTrails excels

• Historical DNS records. Years of archived DNS changes — who pointed where, when. Invaluable for incident response (what IP did this hostname resolve to when the breach occurred?), threat hunting (what other domains shared this infrastructure?), and M&A due diligence (what does the target company's historical attack surface look like?).
• WHOIS history. Registrant information over time, including historical ownership data that is no longer in live WHOIS records. Essential for attribution research and tracking infrastructure evolution.
• Passive DNS at scale. SecurityTrails' passive DNS dataset is one of the most comprehensive commercial offerings — broad coverage, long retention, and programmatic access for bulk queries.
• Enterprise integrations. Native connectors for Splunk, Cortex XSOAR, and other enterprise SIEM/SOAR platforms. For security operations centers that manage investigation workflows programmatically, this matters.
• API quality and SLA. Well-documented REST API, consistent uptime, enterprise support tiers with SLA guarantees. For production tooling that depends on reliable data access, that infrastructure has real value.

Where SubDomainsFinder has the edge

• Completely free, no monthly quota. SecurityTrails' 50-query free tier runs out within a single investigation on a moderately complex target. SubDomainsFinder has no quota, no account, and no paywall hiding rows in the result set.
• No account required. Even SecurityTrails' free tier requires email signup. SubDomainsFinder returns results without any identity — no account tied to your scan history, no upsell email, no tracking.
• Faster for one-off lookups. Even with an active SecurityTrails account, you authenticate, navigate, query, and wait for pagination. With SubDomainsFinder you paste a domain and have results — usually within seconds — without context-switching into a platform.
• Open ports and CDN/WAF detection per subdomain. SecurityTrails shows subdomain names and IPs but not open ports or hosting/CDN context. SubDomainsFinder returns that detail inline per subdomain — useful for immediate triage on which assets deserve closer attention.
• Privacy by default. No account means no scan history sitting in a SaaS tenant tied to your email. For sensitive reconnaissance or users in jurisdictions where active scanning is legally fraught, this matters.

Which tool is right for you?

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