certificate-transparency

Query crt.sh Certificate Transparency logs and extract deduplicated subdomains from SANs.

Updated May 27, 2026
One-click install
npx skills add https://github.com/hoanghn61/.agents --skill certificate-transparency
Or copy as Structured Prompt for Agent
Please help me install this Agent Skill.
Skill: certificate-transparency
Source: https://github.com/hoanghn61/.agents/tree/main/skills/techstack-identification/certificate_transparency
Command: npx skills add https://github.com/hoanghn61/.agents --skill certificate-transparency

SYSTEM DOCUMENTATION & REQUIREMENTS

What problem does it solve?

Certificate Transparency (CT) logs often reveal how a domain is actually used in the wild, but manually searching and extracting subject alternative names (SANs) is time-consuming and error-prone.

Core Features & Use Cases

  • Query CT logs for certificates: Retrieves certificate records from crt.sh for a target domain and collects issuer and validity metadata.
  • Extract and validate SAN-based subdomains: Splits and deduplicates SAN entries to produce a clean list of unique subdomains for reconnaissance.
  • Detect naming patterns and wildcard usage: Infers internal conventions via regex patterns and flags wildcard certificate scopes to highlight potential security exposure.
  • Use Case: Find previously unknown subdomains and infer environment/service naming conventions for a given domain to support security review and asset inventory.

Quick Start

Use the skill to analyze certificates for example.com and return unique subdomains, detected naming patterns, issuer counts, and wildcard certificate findings.

Frequently Asked Questions about certificate-transparency

High-intent search queries and answers about installing and using this skill.

FAQPage Schema
How do I discover subdomains from Certificate Transparency logs?

Discover subdomains from Certificate Transparency logs by querying crt.sh for a target domain and extracting Subject Alternative Names. This process retrieves certificate records, parses SANs, and deduplicates entries to produce a clean inventory of unique subdomains for reconnaissance.

What is the best way to extract Subject Alternative Names for reconnaissance?

Extracting Subject Alternative Names for reconnaissance involves parsing public CT log JSON data and deduplicating entries. This approach identifies unique subdomains, detects naming pattern conventions via regex, and flags wildcard certificate scopes to highlight potential security exposure.

How does wildcard certificate detection work in CT logs?

Wildcard certificate detection in CT logs works by querying crt.sh, parsing certificate records, and flagging wildcard scopes within Subject Alternative Names. This highlights broad certificate usage that may expose multiple subdomains to potential security risks during asset discovery workflows.

Can I use crt.sh JSON data for asset discovery and security auditing?

You can use crt.sh JSON data for asset discovery and security auditing by fetching certificate records with wildcard filtering. The data is parsed to enumerate active subdomains, extract issuer metadata, and validate domain inventory for incident response scoping.

Does querying Certificate Transparency logs require rate-limit-aware behavior?

Querying Certificate Transparency logs requires rate-limit-aware behavior when fetching JSON from crt.sh. Applying wildcard filtering and parsing Subject Alternative Names with rate-limit awareness ensures reliable subdomain enumeration without triggering source restrictions during reconnaissance workflows.

How do I detect naming pattern conventions from SAN entries?

Detect naming pattern conventions from SAN entries involves applying regex detection to parsed and deduplicated Subject Alternative Names extracted from CT logs. This infers internal environment and service naming conventions to support security review and domain inventory validation.