Censys API
Search engine for internet-connected hosts, certificates, and domains, providing structured data on open ports, TLS certificates, and service banners for attack surface management and security research.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
Basic Auth with API ID/Secret pair over HTTPS. No scope granularity — a single credential has full API access. TLS enforced everywhere. Python SDK actively maintained. No public SOC2 or compliance certifications for the search API.
⚡ Reliability
Best When
A security agent needs high-quality certificate intelligence, structured host data, or comprehensive asset discovery via domain and certificate pivoting — especially for attack surface management programs.
Avoid When
You need real-time data, internal network scanning, or your budget can't accommodate the paid tier for meaningful query volume.
Use Cases
- • Discovering all internet-facing assets belonging to an organization via certificate and domain pivoting
- • Enumerating TLS certificate data to find shadow IT and unknown subdomains
- • Correlating host and certificate data for comprehensive attack surface management
- • Enriching security investigations with service and port data for specific IP ranges
- • Monitoring for certificate issuance events related to an organization's domains
Not For
- • Real-time or live network scanning (Censys data reflects periodic scan cycles, not live state)
- • Internal network visibility (covers only internet-facing assets)
- • Teams needing Shodan's broader device/IoT scanning depth (Censys focuses on structured host data and certificates)
- • High-volume free queries — 250 queries/month is very limited for automated agent use
Interface
Authentication
HTTP Basic Auth using API ID as username and API Secret as password. No scopes — key grants access to all endpoints within the account's tier. Credentials available in the Censys account dashboard.
Pricing
Free tier is extremely limited for agent use — 250 queries/month can be exhausted in minutes. The jump from free to paid is significant. Censys ASM (Attack Surface Management) is a separate, higher-cost product.
Agent Metadata
Known Gotchas
- ⚠ 250 free queries/month can be exhausted within a single agent session — paid tier is effectively required for any meaningful automation
- ⚠ Censys query DSL uses a different syntax from Shodan — agents trained on Shodan filters will generate invalid Censys queries
- ⚠ Certificate search and host search are separate indices with different query fields — must use the right endpoint
- ⚠ Data freshness varies — scan data may be days old for less-frequently scanned IP ranges
- ⚠ Python SDK cursor-based pagination requires careful iteration to avoid re-fetching pages on retry
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for Censys API.
Scores are editorial opinions as of 2026-03-06.