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---67# Domain Intelligence — Passive OSINT89Passive domain reconnaissance using only Python stdlib.10**Zero dependencies. Zero API keys. Works on Linux, macOS, and Windows.**1112## Helper script1314This skill includes `scripts/domain_intel.py` — a complete CLI tool for all domain intelligence operations.1516```bash17# Subdomain discovery via Certificate Transparency logs18python SKILL_DIR/scripts/domain_intel.py subdomains example.com1920# SSL certificate inspection (expiry, cipher, SANs, issuer)21python SKILL_DIR/scripts/domain_intel.py ssl example.com2223# WHOIS lookup (registrar, dates, name servers — 100+ TLDs)24python SKILL_DIR/scripts/domain_intel.py whois example.com2526# DNS records (A, AAAA, MX, NS, TXT, CNAME)27python SKILL_DIR/scripts/domain_intel.py dns example.com2829# Domain availability check (passive: DNS + WHOIS + SSL signals)30python SKILL_DIR/scripts/domain_intel.py available coolstartup.io3132# Bulk analysis — multiple domains, multiple checks in parallel33python SKILL_DIR/scripts/domain_intel.py bulk example.com github.com google.com34python SKILL_DIR/scripts/domain_intel.py bulk example.com github.com --checks ssl,dns35```3637`SKILL_DIR` is the directory containing this SKILL.md file. All output is structured JSON.3839## Available commands4041| 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 |4950## When to use this vs built-in tools5152- **Use this skill** for infrastructure questions: subdomains, SSL certs, WHOIS, DNS records, availability53- **Use `web_search`** for general research about what a domain/company does54- **Use `web_extract`** to get the actual content of a webpage55- **Use `terminal` with `curl -I`** for a simple "is this URL reachable" check5657| 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 |6768## Platform compatibility6970Pure Python stdlib (`socket`, `ssl`, `urllib`, `json`, `concurrent.futures`).71Works identically on Linux, macOS, and Windows with no dependencies.7273- **crt.sh queries** use HTTPS (port 443) — works behind most firewalls74- **WHOIS queries** use TCP port 43 — may be blocked on restrictive networks75- **DNS queries** use Google DoH (HTTPS) for MX/NS/TXT — firewall-friendly76- **SSL checks** connect to the target on port 443 — the only "active" operation7778## Data sources7980All queries are **passive** — no port scanning, no vulnerability testing:8182- **crt.sh** — Certificate Transparency logs (subdomain discovery, HTTPS only)83- **WHOIS servers** — Direct TCP to 100+ authoritative TLD registrars84- **Google DNS-over-HTTPS** — MX, NS, TXT, CNAME resolution (firewall-friendly)85- **System DNS** — A/AAAA record resolution86- **SSL check** is the only "active" operation (TCP connection to target:443)8788## Notes8990- WHOIS queries use TCP port 43 — may be blocked on restrictive networks91- Some WHOIS servers redact registrant info (GDPR) — mention this to the user92- crt.sh can be slow for very popular domains (thousands of certs) — set reasonable expectations93- The availability check is heuristic-based (3 passive signals) — not authoritative like a registrar API9495---9697*Contributed by [@FurkanL0](https://github.com/FurkanL0)*
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