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 skills add helderberto/agent-skills --skill hardengit clone --depth 1 https://github.com/helderberto/agent-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/helderberto/agent-skills/harden)<a href="https://agentmods.dev/skills/helderberto/agent-skills/harden"><img src="https://agentmods.dev/badge/skills/helderberto/agent-skills/harden.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 | $0.00077 | $0.00813 |
| Opus 5 | $0.00039 | $0.00407 |
| Sonnet 5 | $0.00015 | $0.00163 |
| Haiku 4.5 | $0.00008 | $0.00081 |
Grade A, and why
harden scanned grade A with 1 finding 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 7d 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.
Makes network callslowCapability
Not a fault in itself. Listed so you know the mod talks to something, and to what.
- [ ] Security headers present in response (check via DevTools or `curl -I`) How it starts
The opening of the file, as written. The whole thing — 83 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Harden
Security as a constraint on every line that touches user data, auth, or external systems. This skill is proactive: applied during implementation, not after. For reactive scans, use safe-repo (sensitive data) or deps-audit (CVEs).
Three-Tier Boundary System
Always do (no exceptions)
- Validate every external input at the system boundary (route handler, API entry)
- Parameterize all database queries (never concatenate user input into SQL)
- Encode output to prevent XSS — use framework auto-escaping, don't bypass it
- HTTPS for all external communication
- Hash passwords with bcrypt/scrypt/argon2 (salt rounds ≥ 12); never plaintext
- Set security headers: CSP, HSTS, X-Frame-Options, X-Content-Type-Options
- Session cookies:
httpOnly,secure,sameSite - Use environment variables for secrets; reference, never inline
- Strip sensitive fields from API responses by default
Ask first (human approval required)
- New authentication flow or auth logic changes
- Storing new categories of sensitive data (PII, payment)
- New external service integrations
- CORS configuration changes
- File upload handlers
- Rate-limit / throttling changes
- Granting elevated permissions or roles
Never do
- Commit secrets to version control
- Log sensitive data (passwords, tokens, full PAN)
- Trust client-side validation as a security boundary
- Disable security headers for convenience
- Use
eval()orinnerHTMLwith user-provided data - Store sessions in client-accessible storage (e.g., localStorage for auth tokens)
- Expose stack traces or internal errors to users
See OWASP Top 10 quick reference.
Input Validation at Boundaries
Always validate at the system boundary (route handler, message consumer), not in business logic:
- Schema validator (Zod, Joi, Yup, pydantic) defines the contract
- Reject with 422 + structured error before any business logic touches the data
- Trust internal code; validate only at the edges
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.
- 7d ago First seen · 83 lines · 77 tokens per session scan A 305efa1693a0
harden is a skill published in the GitHub repository helderberto/agent-skills (14 stars, last pushed 5d ago), licensed MIT. It adds 77 tokens to every session and 813 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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