CertObserver CT Search review covering how this free Certificate Transparency log lookup tool works, its search and grouping features, and the paid…
Certificate Transparency exists because of a hard lesson the web PKI ecosystem learned over the past decade: certificate authorities occasionally issue certificates incorrectly, fraudulently, or without a domain owner's knowledge, and without a public audit trail, these mis-issued certificates could go undetected for long periods, enabling man-in-the-middle attacks or impersonation. CT logs solve this by requiring every publicly trusted certificate to be submitted to one or more append-only, cryptographically verifiable public logs before major browsers will treat it as valid, effectively creating a permanent, searchable public record of every certificate ever issued for every domain on the web. CertObserver's CT Search tool provides a search interface over this data specifically, letting anyone type in a domain and see every historical and currently valid certificate that has been logged for it.
Beyond the straightforward defensive use case of a domain owner checking what certificates exist for their own domains, CT log search has become a standard technique in security research and reconnaissance, since certificates issued for subdomains reveal those subdomains' existence even when they aren't linked anywhere publicly discoverable. A staging server, an internal admin panel, or a forgotten test environment might never show up in a search engine, but if a publicly trusted certificate was ever issued for its hostname, it will appear in CT logs. CertObserver's search and grouping options, filtering by exact match versus subdomain coverage, and grouping by SAN set or issuer, are specifically designed to make this kind of investigative search more efficient than working with raw, ungrouped CT log data.
CertObserver's CT Search is explicitly free with no signup required, and the company frames it as a standalone public resource rather than a gated trial. This positions it similarly to well-established free tools like crt.sh, which has long served as a default reference for manual CT log lookups, though CertObserver's added grouping, deduplication, and near-real-time (roughly 10-minute) ingestion aim to make the experience faster and less noisy for users searching domains with large certificate histories.
The free tool serves as a natural on-ramp to CertObserver's commercial product, also branded CertObserver, which shifts from one-off manual search to continuous, automated monitoring. The paid platform maintains a persistent inventory of an organization's certificates with tags and notes, runs ongoing CT monitors that alert the team the moment a new certificate appears for their domains (whether expected or potentially unauthorized), and separately runs endpoint monitors that actively poll live websites and APIs to confirm the certificates actually being served are valid and not approaching expiration. Pricing for this paid tier is structured across four plans, Small at 9 dollars per month up to Max at 99 dollars per month, scaling primarily by how many certificates, monitors, and team members an organization needs, which keeps the entry price low relative to enterprise certificate lifecycle management suites while still supporting meaningfully larger security or IT teams at the top tier.
Yes. CertObserver's CT Search tool is completely free to use and does not require signup or a credit card. It is offered as a standalone public tool alongside CertObserver's separate paid monitoring platform.
Certificate Transparency is a framework requiring publicly trusted SSL/TLS certificates to be recorded in public, append-only logs before major browsers will trust them, creating a searchable public record of every certificate issued for every domain, which helps detect mis-issued or fraudulent certificates.
Yes. Because any certificate issued for a subdomain must be logged publicly, searching CT logs is a common technique for discovering subdomains, including staging servers or internal tools, that were never linked anywhere publicly discoverable.
Both let users search public Certificate Transparency logs by domain for free, but CertObserver adds features like flexible search scope (exact match, host coverage, subdomain matching), result grouping by SAN set or issuer, and automatic deduplication of pre-certificates and final certificates to make large result sets easier to review.
According to the company, newly issued certificates typically appear in CT Search results within about 10 minutes of issuance.
The paid CertObserver platform adds a persistent certificate inventory, continuous CT monitors that alert on new certificates for your domains, active endpoint monitors that check live sites and APIs, and email and Slack alerting, none of which are included in the free standalone search tool.
CertObserver's paid plans range from $9/month (Small) to $99/month (Max), scaling by the number of inventory certificates, CT monitors, endpoint monitors, and user accounts included, with a 14-day free trial requiring no credit card on all paid tiers.
CertObserver is made by Kodhaj AB, a small Swedish software company.