Domain Intelligence — Passive OSINT
Passive domain reconnaissance using only Python stdlib.
Zero dependencies. Zero API keys. Works on Linux, macOS, and Windows.
Helper script
This skill includes scripts/domain_intel.py — a complete CLI tool for all domain intelligence operations.
# Subdomain discovery via Certificate Transparency logs
python SKILL_DIR/scripts/domain_intel.py subdomains example.com
# SSL certificate inspection (expiry, cipher, SANs, issuer)
python SKILL_DIR/scripts/domain_intel.py ssl example.com
# WHOIS lookup (registrar, dates, name servers — 100+ TLDs)
python SKILL_DIR/scripts/domain_intel.py whois example.com
# DNS records (A, AAAA, MX, NS, TXT, CNAME)
python SKILL_DIR/scripts/domain_intel.py dns example.com
# Domain availability check (passive: DNS + WHOIS + SSL signals)
python SKILL_DIR/scripts/domain_intel.py available coolstartup.io
# Bulk analysis — multiple domains, multiple checks in parallel
python SKILL_DIR/scripts/domain_intel.py bulk example.com github.com google.com
python SKILL_DIR/scripts/domain_intel.py bulk example.com github.com --checks ssl,dns
SKILL_DIR is the directory containing this SKILL.md file. All output is structured JSON.
Available commands
| Command |
What it does |
Data source |
subdomains |
Find subdomains from certificate logs |
crt.sh (HTTPS) |
ssl |
Inspect TLS certificate details |
Direct TCP:443 to target |
whois |
Registration info, registrar, dates |
WHOIS servers (TCP:43) |
dns |
A, AAAA, MX, NS, TXT, CNAME records |
System DNS + Google DoH |
available |
Check if domain is registered |
DNS + WHOIS + SSL signals |
bulk |
Run multiple checks on multiple domains |
All of the above |
When to use this vs built-in tools
- Use this skill for infrastructure questions: subdomains, SSL certs, WHOIS, DNS records, availability
- Use
web_search for general research about what a domain/company does
- Use
web_extract to get the actual content of a webpage
- Use
terminal with curl -I for a simple "is this URL reachable" check
| Task |
Better tool |
Why |
| "What does example.com do?" |
web_extract |
Gets page content, not DNS/WHOIS data |
| "Find info about a company" |
web_search |
General research, not domain-specific |
| "Is this website safe?" |
web_search |
Reputation checks need web context |
| "Check if a URL is reachable" |
terminal with curl -I |
Simple HTTP check |
| "Find subdomains of X" |
This skill |
Only passive source for this |
| "When does the SSL cert expire?" |
This skill |
Built-in tools can't inspect TLS |
| "Who registered this domain?" |
This skill |
WHOIS data not in web search |
| "Is coolstartup.io available?" |
This skill |
Passive availability via DNS+WHOIS+SSL |
Platform compatibility
Pure Python stdlib (socket, ssl, urllib, json, concurrent.futures).
Works identically on Linux, macOS, and Windows with no dependencies.
- crt.sh queries use HTTPS (port 443) — works behind most firewalls
- WHOIS queries use TCP port 43 — may be blocked on restrictive networks
- DNS queries use Google DoH (HTTPS) for MX/NS/TXT — firewall-friendly
- SSL checks connect to the target on port 443 — the only "active" operation
Data sources
All queries are passive — no port scanning, no vulnerability testing:
- crt.sh — Certificate Transparency logs (subdomain discovery, HTTPS only)
- WHOIS servers — Direct TCP to 100+ authoritative TLD registrars
- Google DNS-over-HTTPS — MX, NS, TXT, CNAME resolution (firewall-friendly)
- System DNS — A/AAAA record resolution
- SSL check is the only "active" operation (TCP connection to target:443)
Notes
- WHOIS queries use TCP port 43 — may be blocked on restrictive networks
- Some WHOIS servers redact registrant info (GDPR) — mention this to the user
- crt.sh can be slow for very popular domains (thousands of certs) — set reasonable expectations
- The availability check is heuristic-based (3 passive signals) — not authoritative like a registrar API
Contributed by @FurkanL0
1---2name: domain-intel3description: Passive recon of subdomains, SSL certs, WHOIS, and DNS.4license: MIT5---6
7# Domain Intelligence — Passive OSINT
8
9Passive domain reconnaissance using only Python stdlib.
10**Zero dependencies. Zero API keys. Works on Linux, macOS, and Windows.**
11
12## Helper script
13
14This skill includes `scripts/domain_intel.py` — a complete CLI tool for all domain intelligence operations.
15
16```bash
17# Subdomain discovery via Certificate Transparency logs
18python SKILL_DIR/scripts/domain_intel.py subdomains example.com
19
20# SSL certificate inspection (expiry, cipher, SANs, issuer)
21python SKILL_DIR/scripts/domain_intel.py ssl example.com
22
23# WHOIS lookup (registrar, dates, name servers — 100+ TLDs)
24python SKILL_DIR/scripts/domain_intel.py whois example.com
25
26# DNS records (A, AAAA, MX, NS, TXT, CNAME)
27python SKILL_DIR/scripts/domain_intel.py dns example.com
28
29# Domain availability check (passive: DNS + WHOIS + SSL signals)
30python SKILL_DIR/scripts/domain_intel.py available coolstartup.io
31
32# Bulk analysis — multiple domains, multiple checks in parallel
33python SKILL_DIR/scripts/domain_intel.py bulk example.com github.com google.com
34python SKILL_DIR/scripts/domain_intel.py bulk example.com github.com --checks ssl,dns
35```
36
37`SKILL_DIR` is the directory containing this SKILL.md file. All output is structured JSON.
38
39## Available commands
40
41| Command | What it does | Data source |
42|---------|-------------|-------------|
43| `subdomains` | Find subdomains from certificate logs | crt.sh (HTTPS) |
44| `ssl` | Inspect TLS certificate details | Direct TCP:443 to target |
45| `whois` | Registration info, registrar, dates | WHOIS servers (TCP:43) |
46| `dns` | A, AAAA, MX, NS, TXT, CNAME records | System DNS + Google DoH |
47| `available` | Check if domain is registered | DNS + WHOIS + SSL signals |
48| `bulk` | Run multiple checks on multiple domains | All of the above |
49
50## When to use this vs built-in tools
51
52- **Use this skill** for infrastructure questions: subdomains, SSL certs, WHOIS, DNS records, availability
53- **Use `web_search`** for general research about what a domain/company does
54- **Use `web_extract`** to get the actual content of a webpage
55- **Use `terminal` with `curl -I`** for a simple "is this URL reachable" check
56
57| Task | Better tool | Why |
58|------|-------------|-----|
59| "What does example.com do?" | `web_extract` | Gets page content, not DNS/WHOIS data |
60| "Find info about a company" | `web_search` | General research, not domain-specific |
61| "Is this website safe?" | `web_search` | Reputation checks need web context |
62| "Check if a URL is reachable" | `terminal` with `curl -I` | Simple HTTP check |
63| "Find subdomains of X" | **This skill** | Only passive source for this |
64| "When does the SSL cert expire?" | **This skill** | Built-in tools can't inspect TLS |
65| "Who registered this domain?" | **This skill** | WHOIS data not in web search |
66| "Is coolstartup.io available?" | **This skill** | Passive availability via DNS+WHOIS+SSL |
67
68## Platform compatibility
69
70Pure Python stdlib (`socket`, `ssl`, `urllib`, `json`, `concurrent.futures`).
71Works identically on Linux, macOS, and Windows with no dependencies.
72
73- **crt.sh queries** use HTTPS (port 443) — works behind most firewalls
74- **WHOIS queries** use TCP port 43 — may be blocked on restrictive networks
75- **DNS queries** use Google DoH (HTTPS) for MX/NS/TXT — firewall-friendly
76- **SSL checks** connect to the target on port 443 — the only "active" operation
77
78## Data sources
79
80All queries are **passive** — no port scanning, no vulnerability testing:
81
82- **crt.sh** — Certificate Transparency logs (subdomain discovery, HTTPS only)
83- **WHOIS servers** — Direct TCP to 100+ authoritative TLD registrars
84- **Google DNS-over-HTTPS** — MX, NS, TXT, CNAME resolution (firewall-friendly)
85- **System DNS** — A/AAAA record resolution
86- **SSL check** is the only "active" operation (TCP connection to target:443)
87
88## Notes
89
90- WHOIS queries use TCP port 43 — may be blocked on restrictive networks
91- Some WHOIS servers redact registrant info (GDPR) — mention this to the user
92- crt.sh can be slow for very popular domains (thousands of certs) — set reasonable expectations
93- The availability check is heuristic-based (3 passive signals) — not authoritative like a registrar API
94
95---
96
97*Contributed by [@FurkanL0](https://github.com/FurkanL0)*
gabrielmoreira