Free real-time Certificate Transparency stream, no API key

CertStream is a free, hosted WebSocket API that streams real-time Certificate Transparency log data, including newly issued TLS certificates and associated domain names. It supports two endpoints: a domains-only stream (~200 bytes per message) and a lite stream (~1 KB per message) that includes additional certificate metadata such as issuer and validity dates. The API requires no authentication or API key, allowing easy integration with existing CertStream clients and libraries. The service reads from Chrome- and Apple-trusted CT logs and delivers each certificate once even if it appears in multiple logs. It is intended for use cases like phishing detection, brand monitoring, subdomain discovery, and threat intelligence pipelines. The public endpoint limits concurrent connections per IP to two and maintains a 99.9% availability SLA. Users can also self-host the full stream with certificate chains if desired.

This is not a vulnerability or exploit but a publicly available data stream providing transparency into newly issued TLS certificates. It enables defenders and researchers to monitor domain registrations and certificate issuance in real time, aiding in early detection of phishing, typosquatting, and other malicious activities. There is no direct security impact or risk from the service itself.

No mitigation is required as this is not a security vulnerability or threat. The service is intentionally public and free to use for security monitoring purposes.