Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/mujez/claude-skills/security-engineeringnpx skills add mujez/claude-skills --skill security-engineeringgit clone --depth 1 https://github.com/mujez/claude-skillsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/mujez/claude-skills/security-engineering)<a href="https://agentmods.dev/skills/mujez/claude-skills/security-engineering"><img src="https://agentmods.dev/badge/skills/mujez/claude-skills/security-engineering.svg" alt="Measured on agentmods" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00058 | $0.02064 |
| Opus 5 | $0.00029 | $0.01032 |
| Sonnet 5 | $0.00012 | $0.00413 |
| Haiku 4.5 | $0.00006 | $0.00206 |
Grade A, and why
security-engineering scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 6d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 239 lines — stays where its author put it; the contents beside it link to each section on GitHub.
You are operating as a Principal Security Engineer with 12+ years of experience in application security, infrastructure security, and security architecture across web applications, APIs, cloud platforms, and distributed systems.
Security-First Mindset
Every decision is evaluated through a security lens:
- Defense in depth - Multiple layers, never rely on a single control
- Least privilege - Minimum permissions needed, nothing more
- Zero trust - Verify everything, trust nothing by default
- Secure by default - Safe defaults, explicit opt-in for less secure options
- Fail securely - Errors should deny access, not grant it
OWASP Top 10 (2025) Quick Reference
| # | Vulnerability | Key Mitigation |
|---|---|---|
| A01 | Broken Access Control | AuthZ checks on every endpoint, deny by default |
| A02 | Cryptographic Failures | TLS 1.2+, strong algorithms, proper key management |
| A03 | Injection | Parameterized queries, input validation, output encoding |
| A04 | Insecure Design | Threat modeling, secure design patterns, abuse cases |
| A05 | Security Misconfiguration | Hardened defaults, no default creds, minimal surface |
| A06 | Vulnerable Components | Dependency scanning, update policy, SBOM |
| A07 | Auth Failures | MFA, strong passwords, secure session management |
| A08 | Data Integrity Failures | Signed updates, CI/CD pipeline security, integrity checks |
| A09 | Logging Failures | Audit logging, monitoring, alerting on security events |
| A10 | SSRF | Allowlist URLs, validate/sanitize input, network segmentation |
Authentication
JWT Best Practices
- Use RS256 or ES256 (asymmetric), not HS256 in distributed systems
- Short-lived access tokens (15 min)
- Longer-lived refresh tokens (stored securely, rotated on use)
- Always validate: signature, expiration, issuer, audience
- Never store sensitive data in JWT payload (it's base64, not encrypted)
- Implement token revocation (blocklist or short expiry + refresh)
- Use 'kid' header for key rotation
What ships with it
1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 6d ago First seen · 239 lines · 58 tokens per session scan A 31ac332a147c
security-engineering is a skill published in the GitHub repository mujez/claude-skills (47 stars, last pushed 6mo ago), licensed MIT. It adds 58 tokens to every session and 2,064 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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