find-hidden-subdomains SKILL.md skillA
find-hidden-subdomains from tonydzi/second-brain-starter-kit is an agent skill: a SKILL.md folder an AI agent loads when a task calls for it.
mdr add tonydzi/second-brain-starter-kit/find-hidden-subdomains@git:20261020.402f6b7Pins git:20261020.402f6b7 in mdr.lock. Pin the fingerprint instead.
- Audit grade
- A, 17 of 17 checks passed
- Kind
- SKILL.md skill
- Repository
- tonydzi/second-brain-starter-kit
- Path
skills/find-hidden-subdomains/SKILL.md- Versions recorded
- 4
- Latest version
- git:20261020.402f6b7, committed Oct 20, 2026
- First version recorded
- Sep 24, 2026
- Size
- 13,656 bytes
- Repository stars
- 14
- License
- MIT
- Enumerate an organisation's subdomains and sibling domains from Certificate Transparency logs and passive DNS, without sending traffic to the target. Use when looking for staging, dev, admin or VPN hosts, mapping the full hostname footprint of a domain, or spotting infrastructure a company forgot it had.
Collected from public GitHub. Every version is saved exactly as it was and never changes. Install it at an exact version with the mdr tool, and every file is checked before it reaches your agent. The main file is checked against the SHA-256 fingerprint recorded here, and the others against the fingerprints GitHub keeps for its source commit. The automatic checks below grade the latest version, and the same checks always give the same file the same grade.
What the file says
# Find hidden subdomains The hosts an organization forgot about are the ones worth finding, and most of them announced themselves the moment someone requested a TLS certificate. Certificate Transparency turns that into a searchable, permanent, historical index — free and completely passive. The beginner's mistake is treating a CT hit as a live host: most of what you pull back does not resolve, and that is information too, not noise. ## Which source first | You hold | Start with | Why | |---|---|---| | An apex domain | crt.sh wildcard query | Broadest free coverage, includes long-dead names | | A domain behind a wildcard cert | Passive DNS, then archives | CT will only show you `*.example.com` | | A guess at a naming convention | CT to learn the convention, then a wordlist | Learn the pattern before brute-forcing anything | | An org name, not a domain | Certificate search by subject organization | Finds domains you did not know they owned | | A cert you already have | Its SANs, then its serial and issuer | SANs give siblings; serial finds the exact cert elsewhere | …
Read the whole file at its exact version.
How to install
mdr add tonydzi/second-brain-starter-kit/find-hidden-subdomains@sha256:7189023c1747f752The line at the top of this page pins the label git:20261020.402f6b7, which is what most people want. This one pins the sha256 fingerprint of the contents instead, so it survives a label being moved. Either way the exact version is written to mdr.lock, and mdr install downloads and checks those contents again, so it installs them exactly or stops with an error.
[](https://markdownregistry.com/a/art_czcijode7uuwngt3)
3 badge image fetches in 30 days. What the badge shows.
Versions
The registry has recorded 4 versions of this file, between Sep 24, 2026 and Oct 20, 2026, about one every 9 days.
| version | committed | commit | size | audit | |
|---|---|---|---|---|---|
| git:20261020.402f6b7 latest | 2026-10-20 | 402f6b7 | 13,656 B | A | view · diff |
| git:20261007.cd6c208 | 2026-10-07 | cd6c208 | 13,662 B | A | view · diff |
| git:20261003.a2d662f | 2026-10-03 | a2d662f | 13,663 B | A | view · diff |
| git:20260924.2784cb2 | 2026-09-24 | 2784cb2 | 12,548 B | A | view |
Audit of the latest version
- pass: Frontmatter block present
- pass: Frontmatter declares a name
- pass: Frontmatter declares a description
- pass: Size between 200 bytes and 200 KB (13656 bytes)
- pass: No zero-width or bidi control characters
- pass: No instruction hidden inside an HTML comment
- pass: No link to an exfiltration or paste host
- pass: No credential-shaped string
- pass: No instruction to send local credentials anywhere
- pass: No text hidden with inline styles
- pass: No prompt-injection phrasing
- pass: No curl or wget piped into a shell
- pass: No recursive delete of root, home or parent
- pass: No instruction to read or print local credentials
- pass: No base64 blob over 200 characters
- pass: No link to a raw IP address
- pass: No script tag
Source
tonydzi/second-brain-starter-kit · 14 stars · license MIT · pushed 2026-11-06 · branch master
API
GET https://markdownregistry.com/api/v1/artifacts/art_czcijode7uuwngt3 GET https://markdownregistry.com/api/v1/resolve?ref=tonydzi/second-brain-starter-kit/find-hidden-subdomains GET https://markdownregistry.com/api/v1/blob/7189023c1747f752a9bbeee9c82d1a4ee1a973ac087c0a6ed74198fc027ddf31
Your AI assistant does the legwork. You hear about the deals worth your word. Hand yours the standing instructions at modelranch.com and it joins the network that reads files like this one.
Guides: the SKILL.md format and its required fields · what to check before you install a skill · how to pin a skill to an exact version · where to find agent skills · keeping a team on the same skills · which agent file does what.