Lookup Censys

lookup-censys

Queries Censys for host and certificate reconnaissance on IPs, or runs a Censys Search query. Retrieval only. Quota-aware — free tier is 250 queries/month.

When to invoke

• Shodan wasn't sufficient and deeper host data is needed
• TLS certificate pivoting (find other hosts sharing a cert)
• Specific Censys Search query required

Do NOT invoke for:

• Bulk enrichment (will exhaust quota)
• IPs you can get from Shodan first

How to invoke

Two CLIs are provided. Pick by capability needed.

> Auth note: Censys migrated to a single Personal Access Token (PAT) on the new Platform. The Node CLI uses the legacy Search API (HTTP Basic Auth with CENSYS_API_ID + CENSYS_API_SECRET); the Python CLI uses the new Platform API (Bearer auth with CENSYS_PAT). New accounts get a PAT — use the Python CLI. Old accounts may still have working legacy credentials and can use either.

Basic host + search — Node CLI (legacy Search API)

node tools/clis/censys.js ip 
node tools/clis/censys.js search ""      # Censys Search syntax

Requires CENSYS_API_ID + CENSYS_API_SECRET (legacy). Hits hosts/{ip} or hosts/search.

Full Platform surface — Python CLI (new Censys Platform SDK)

python3 tools/clis/censys.py host  [--at-time ISO8601]
python3 tools/clis/censys.py timeline  --start ISO8601 --end ISO8601
python3 tools/clis/censys.py services 
python3 tools/clis/censys.py search "" [--page-size N] [--page-token TOKEN] [--fields F1,F2]
python3 tools/clis/censys.py aggregate "" --field FIELD [--buckets N] [--filter-by-query]
python3 tools/clis/censys.py certs view 
python3 tools/clis/censys.py certs list 

Requires CENSYS_PAT (new). Self-bootstraps a private venv at tools/clis/.venv-censys/ on first run (installs censys-platform).

Capabilities the Node CLI doesn't have, ordered by CTI value:

1. Aggregate — the unsung hero. Aggregations are free (do not consume query credits) and let you ask "how many hosts in this query break down by country / port / ASN / product?" in a single call. Use this BEFORE a search to scope the result set without spending credits.
2. Host timeline — the activity history of a single IP between two timestamps. New in Platform.
3. At-time host view — see what a host looked like at a past timestamp (Platform-only).
4. Service listing — enumerate just the services on a host without the full record.
5. Certificate view by ID + certificate list (bulk) — pull cert detail or batch fetch.
6. Cursor-based pagination — --page-token for traversing large result sets.

Examples:

# Free aggregation: count hosts running Cobalt Strike by country (no credits)
python3 tools/clis/censys.py aggregate \
  'services.product: "Cobalt Strike Team Server"' \
  --field location.country_code

# Free aggregation: ASN distribution of a JARM-fingerprinted cluster
python3 tools/clis/censys.py aggregate \
  'services.tls.jarm.fingerprint: "1234567890abcdef..."' \
  --field autonomous_system.asn --buckets 50

# What was this IP doing two weeks ago? (Platform-only)
python3 tools/clis/censys.py host 185.220.101.45 \
  --at-time 2026-04-12T00:00:00Z

# Daily activity timeline for an IP
python3 tools/clis/censys.py timeline 185.220.101.45 \
  --start 2026-04-01T00:00:00Z --end 2026-04-26T00:00:00Z

# Certificate view by ID (the SHA-256 fingerprint)
python3 tools/clis/censys.py certs view 5e884898da28047151d0e56f8dc6292773603d0d6aabbdd62a11ef721d1542d8

# Search hosts and only return specific fields (saves payload)
python3 tools/clis/censys.py search \
  'services.tls.certificates.leaf_data.subject.common_name: "*.badcorp.example"' \
  --fields ip,location.country_code,services.port

Both CLIs accept --dry-run. Python CLI exits code 2 if CENSYS_PAT is unset; Node CLI exits code 2 if either of the legacy variables is unset. Report missing credentials; do not fabricate.

Free tier reality check (Platform API)

The new Censys Platform tightened free-tier API access. As of 2026, free Community accounts can call these endpoints only:

• host — view host detail by IP ✓
• services — list services on a host ✓
• timeline — host activity timeline between two timestamps ✓
• certs view — certificate by ID ✓

These are restricted on free tier (return 403 "endpoint requires organization ID"):

• search — paid plan with organization required
• aggregate — paid plan only (no longer free as it was on the legacy API)
• certs list — likely same restriction

For search / aggregation / pivoting on a free account, use the Censys web UI at https://platform.censys.io/. The web UI has full access; API access for those endpoints is a paid feature.

For CLI use on free tier, the Python CLI is still useful for per-IP enrichment (host, services, timeline) but won't replace the legacy Search API's free aggregations. If you have a legacy account with CENSYS_API_ID + CENSYS_API_SECRET, the Node CLI may give you better free-tier reach for now.

Credits (free tier)

Each per-IP call on a free account counts against the 250 queries/month quota. Be deliberate.

When to use Censys vs Shodan

For bulk infrastructure mapping, prefer Shodan — its free-membership tier ($49 one-time) gives you proper search access, and count is free. Reserve Censys for high-fidelity per-IP enrichment of indicators you've already found elsewhere.

Response format

source: censys
indicator: 
query_time: 
services:
  - port: 
    service: 
    banner: 
certificates:
  - subject_cn: 
    issuer: 
    sha256: 
autonomous_system:
  asn: 
  name: 
location:
  country: 
  city: 
last_updated: 

Rate limits

Free tier: 250 queries/month (very limited). Research tier: 10k/month. Paid: unlimited.

Source reliability (Admiralty default)

Default rating for downstream /score-source: A2 (completely reliable, probably true). Censys is an authoritative internet-scan dataset with strong data hygiene.

Operational notes

• Quota conservation is critical. Before invoking, consider whether Shodan can answer the question first.
• For certificate pivoting specifically, Censys is often the right first call — Shodan has weaker cert data.
• Uses HTTP Basic Auth with $CENSYS_API_ID and $CENSYS_API_SECRET.

Related skills

• /lookup-shodan — lighter-weight alternative with higher rate limits
• /lookup-virustotal — reputation, not reconnaissance
• /ip-investigation

See also

• Integration setup: tools/integrations/censys.md
• Node CLI source: tools/clis/censys.js
• Python CLI source: tools/clis/censys.py
• Official Python SDK: https://github.com/censys/censys-sdk-python
• API docs: https://docs.censys.com/reference/get-started
• Search syntax: https://search.censys.io/search/language

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: Liberty91LTD
• Source: Liberty91LTD/cti-skills
• License: MIT
• Homepage: https://liberty91.com/cti-skills

Install and usage instructions live in the source repository linked above.