domain-infra-history
Censys Search
An internet-wide scanning index of hosts and certificates, similar in role to Shodan. Searching is done through its web interface; an API with a free tier exists but requires a key, so it is linked here rather than queried. Relevant when investigating what a host or domain exposes to the internet and its certificate footprint. Currently degraded, the site may put a CAPTCHA in your way.
No programmatic check, opens the archive’s own search.
Why it’s useful & how it works
Censys is useful when you want to understand what a host or domain exposes to the open internet: open ports, running services, TLS certificate chains, and how that picture has changed over time. It continuously scans the entire routable IPv4 address space across more than 200 protocols and 65,000 ports. Echo links you to its search interface and you run queries there; a free-tier API exists for programmatic use but requires registration.
What’s inside
Censys currently indexes around 225 million IPv4 hosts, 1.4 billion virtual hosts, and 2.8 billion services, making it one of the most comprehensive snapshots of the live internet's attack surface. It also maintains a large continuously updated certificate dataset drawn from CT logs.
API access
https://search.censys.io/api (key; free tier)
An API key is required (usually free); see the endpoints above for where to get one.
What we measured
Our own probes, not the archive’s own claims. Re-run periodically; every reading below is dated.
Reachability
- Direct request
- Cloudflare challenge HTTP 403 268 ms (just a moment)
- Through a datacenter proxy
- Cloudflare challenge HTTP 403 478 ms (just a moment)
- API, direct
- Cloudflare challenge HTTP 403 19 ms (just a moment)
- API, through a proxy
- Cloudflare challenge HTTP 403 514 ms (just a moment)
Reachability measured 2026-08-22.
Access
May require solving a captcha before it responds.