Find the subdomains of any domain
Enter a domain name to instantly reveal the subdomains discovered for it, from one of the largest subdomain indexes anywhere.
Enter a root domain like example.com.
Built for automation: the JSON API
Query the same subdomain data from your scripts and pipelines. One endpoint, no signup, no API key, JSON out.
Read the API docs →Use it in your AI agent: MCP server
Look up subdomains as a native tool over the Model Context Protocol. No key, no signup. Works with Claude, Cursor, VS Code, Gemini, Codex, ChatGPT, and more.
Read the MCP docs →One lookup. Known subdomains, surfaced fast.
- One of the largest indexes anywhere. Billions of subdomains gathered across the internet, searchable in milliseconds.
- No active scanning. The target is never scanned or contacted. Results come straight from the index, so nothing is sent to the domain being looked up.
- Instant & free. No signup, no account, no API key. Just enter a domain.
- Built for automation. A clean JSON API, plus an MCP server for AI agents, serves the same data to scripts and pipelines.
What to enter
Enter any domain and Subdomain API reduces it to its
registrable domain automatically — paste a full
URL, a www. prefix, a path, or a subdomain and it just works.
- example.com
- my-company.co.uk
- https://www.example.com/about (→ example.com)
- blog.example.com (→ example.com)
What's returned
- Up to 10,000 subdomains per domain, most recently seen first, paginated 1,000 at a time.
- The same results as JSON from
api.subdomain.app/v1/query.
Who it's for
- Security & recon. Map a target's attack surface and surface forgotten assets during pentests and bug-bounty research.
- IT & ops. Inventory the subdomains tied to a brand and catch shadow IT.
- SEO & monitoring. Understand a domain's footprint and track how it changes over time.
Good to know
The index is both historic and current. Some subdomains may have existed at one point and may no longer resolve today, while others have only just been observed. Coverage is broad but never guaranteed complete or real time, so a subdomain that isn't listed may simply not have been seen yet. Only the queried domains are stored, with no personal data; see the privacy policy.
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Disclaimer
This website is developed by technical SEO consultant and ex-Google engineer Fili.
Bugs will happen, and despite best efforts to maintain the code base and data quality, completeness and accuracy cannot be guaranteed. This is a personal website and for-fun project. Results are passive, best-effort lookup data collected from multiple sources over time. They may be incomplete, outdated, or inaccurate. Please verify results independently before relying on them. See the Terms for details.