cduggn SKILL.md Content Security Analyzer
Contents
- Quick start
- Analysis workflow
- Understanding results
- Example output
- Validation loop
- Threat reference → See THREATS.md
Quick Start
/skill-check <file.md>
Where <file.md> is a path to a SKILL.md file to analyze.
Analysis Workflow
Copy and track progress:
SKILL.md Security Analysis:
- [ ] Step 1: Obtain SKILL.md file to analyze
- [ ] Step 2: Build and run the analyzer
- [ ] Step 3: Review signal (SAFE / SUSPICIOUS / DANGEROUS)
- [ ] Step 4: Investigate any HIGH or MEDIUM findings
- [ ] Step 5: Make adoption decision
Understanding Results
Signal Levels
| Signal | Meaning |
|---|---|
| SAFE | No security concerns detected — safe to install with standard review |
| SUSPICIOUS | Medium-severity findings detected — investigate before installing |
| DANGEROUS | High-severity findings detected — do not install without thorough manual review |
Detection Layers
| Layer | What It Detects |
|---|---|
| unicode | Trojan source (BiDi chars), invisible characters, variation selectors, homoglyphs |
| structure | Missing/malformed frontmatter, dangerous URI schemes, suspicious links |
| injection | Prompt injection patterns, hidden HTML comments, encoding payloads |
| coherence | Suspicious action verbs, frontmatter-to-instructions mismatch, self-contradictions |
Severity Levels
| Severity | Meaning |
|---|---|
| HIGH | Critical threat — triggers DANGEROUS signal |
| MEDIUM | Notable concern — triggers SUSPICIOUS signal |
| LOW | Minor issue — informational |
| INFO | Structural observation — no security impact |
Example Output
# SKILL.md Security Report: suspicious-skill/SKILL.md
## Signal: DANGEROUS
**Findings:** 3
### HIGH Severity (2)
**1. [unicode] bidi-control**
- Line 45, Section: Instructions
- Bidirectional control character U+202E detected (Trojan Source attack vector)
- Evidence: `position 12 in line`
**2. [injection] injection-override**
- Line 52, Section: Instructions
- Direct prompt injection: attempts to override previous instructions
- Evidence: `ignore all previous instructions and instead...`
### MEDIUM Severity (1)
**1. [coherence] suspicious-verbs**
- Line 30, Section: Instructions
- Instructions section contains suspicious action verbs: delete, exfiltrate
- Evidence: `delete, exfiltrate`
Validation Loop
- Run analysis:
/skill-check <file.md> - Review the signal level
- If SUSPICIOUS or DANGEROUS:
- Review each finding and its evidence
- Check the line numbers in the original file
- Determine if findings are true positives or false positives
- For skill adoption:
- SAFE → proceed with standard code review
- SUSPICIOUS → investigate flagged areas, verify intent
- DANGEROUS → reject or require expert manual review
- Combine with
/repo-checkfor full trust assessment
Instructions
When the user invokes this skill:
Identify the SKILL.md file to analyze. If the user provides a URL, download it first. If they provide a local path, use it directly.
Build and run the analyzer binary:
cd skill-check && go build -o skill-check . && ./skill-check <file.md>For JSON output:
cd skill-check && go build -o skill-check . && ./skill-check --json <file.md>Present the structured report to the user, highlighting:
- The overall signal (SAFE / SUSPICIOUS / DANGEROUS)
- Any HIGH or MEDIUM severity findings with evidence
- Which detection layer flagged each concern
For SUSPICIOUS or DANGEROUS results, provide guidance:
- Explain what each finding means in plain language
- Suggest whether the finding is likely a true positive or false positive
- Recommend next steps (reject, investigate further, or accept with caveats)
If the Go binary is unavailable, inform the user that Go 1.24+ is required and provide install instructions.
Recommend combining with
/repo-checkto assess both content safety and repository trust signals for a complete evaluation.