Developer Reference

Subdomain Finder API Documentation

Subdomain Finder API Documentation: Discover subdomains using Certificate Transparency (CT) logs. Use prefer_cache=1 to poll cached results: cold misses return HTTP 202, queue a background refresh, and do not consume credits.

Subdomain Finder

Discover subdomains using Certificate Transparency (CT) logs. Use prefer_cache=1 to poll cached results: cold misses return HTTP 202, queue a background refresh, and do not consume credits.

GET /v1/subdomains

Query Parameters

Parameter	Type	Description
domain required	string	Root domain to find subdomains for (e.g., "github.com")
prefer_cache optional	boolean	Serve cached results only. If no fresh or stale cache exists, the API returns 202, queues a background refresh, and charges 0 credits.
sources optional	string	Comma-separated data sources. Currently only `ct` (Certificate Transparency) is accepted.
verify optional	boolean	Verify each subdomain resolves via DNS (slower but more accurate). Default: `false`
limit optional	number	Maximum subdomains to return. Default: 500, Max: 2000

Use Cases

Attack surface mapping and security audits
Discover forgotten or shadow IT subdomains
Pre-acquisition technical due diligence
Competitive analysis of infrastructure
Bug bounty reconnaissance

Response Fields

Field	Description
`subdomains[].name`	The discovered subdomain hostname
`subdomains[].source`	Data source (e.g., "ct")
`subdomains[].first_seen`	When this subdomain was first observed
`subdomains[].verified`	Whether DNS resolution was confirmed (if verify=true)
`subdomains[].dns_records`	DNS records found (if verify=true)
`summary.total_found`	Total subdomains discovered before limit
`summary.verified_count`	Number of verified (live) subdomains

HTTP Status Codes

HTTP Status Codes	Description
`200` OK	Request successful
`202` Accepted	Cache-only subdomain miss accepted for background refresh. No credits are charged; retry after the Retry-After delay.
`400` Bad Request	Invalid parameters
`402` Payment Required	Not enough credits to run this request.
`503` Service Unavailable	Upstream service unavailable or temporarily rate limited.
`504` Gateway Timeout	Upstream lookup timed out.

Example Request

# Find subdomains (fast, from CT logs)
curl "https://domscan.net/v1/subdomains?domain=github.com&limit=100"

# Find and verify subdomains (slower, confirms DNS resolution)
curl "https://domscan.net/v1/subdomains?domain=github.com&verify=true&limit=50"

curl "https://domscan.net/v1/subdomains?domain=github.com&prefer_cache=1"

import requests

# Enumerate subdomains with verification
response = requests.get(
    "https://domscan.net/v1/subdomains",
    params={
        "domain": "github.com",
        "verify": "true",
        "limit": 100
    }
)
data = response.json()

print(f"Found {data['summary']['total_found']} subdomains")
print(f"Verified: {data['summary']['verified_count']}")

# Filter to only live subdomains
live_subs = [s for s in data['subdomains'] if s['verified']]
for sub in live_subs[:10]:
    print(f"  {sub['name']}")

const response = await fetch(
  'https://domscan.net/v1/subdomains?' + new URLSearchParams({
    domain: 'github.com',
    verify: 'true',
    limit: '100'
  })
);
const data = await response.json();

console.log(`Found ${data.summary.total_found} subdomains`);
console.log(`Verified: ${data.summary.verified_count}`);

// List verified subdomains
data.subdomains
  .filter(s => s.verified)
  .forEach(s => console.log(`  ${s.name}`));

Example Response

{
  "domain": "github.com",
  "subdomains": [
    {
      "name": "api.github.com",
      "source": "ct",
      "first_seen": "2024-01-15T00:00:00Z",
      "verified": true,
      "dns_records": ["A 140.82.112.5"]
    },
    {
      "name": "gist.github.com",
      "source": "ct",
      "first_seen": "2024-02-01T00:00:00Z",
      "verified": true,
      "dns_records": ["CNAME github.github.io"]
    },
    {
      "name": "education.github.com",
      "source": "ct",
      "first_seen": "2023-06-10T00:00:00Z",
      "verified": true,
      "dns_records": ["A 185.199.108.153"]
    }
  ],
  "summary": {
    "total_found": 847,
    "returned": 3,
    "verified_count": 3,
    "unverified_count": 0,
    "sources_used": ["ct"]
  },
  "meta": {
    "query_time_ms": 1250,
    "cached": false
  }
}

202 Accepted

{
  "status": "pending",
  "code": "CACHE_MISS_REFRESH_QUEUED",
  "message": "Try again in a moment",
  "domain": "github.com",
  "retry_after": 30,
  "credits_charged": 0,
  "billing_status": "not_charged",
  "request_id": "m8abc12-x9y8"
}