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 HoangNguyen0403/agent-skills-standard --skill common-agent-guardrailsgit clone --depth 1 https://github.com/HoangNguyen0403/agent-skills-standardWrote 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/hoangnguyen0403/agent-skills-standard/common-agent-guardrails)<a href="https://agentmods.dev/skills/hoangnguyen0403/agent-skills-standard/common-agent-guardrails"><img src="https://agentmods.dev/badge/skills/hoangnguyen0403/agent-skills-standard/common-agent-guardrails/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/hoangnguyen0403/agent-skills-standard/common-agent-guardrails"><img src="https://agentmods.dev/badge/skills/hoangnguyen0403/agent-skills-standard/common-agent-guardrails.svg" alt="Reviewed on agentmods" width="80" 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 | $0.00060 | $0.01008 |
| Opus 5.5 | $0.00024 | $0.00403 |
| Sonnet 5.5 | $0.00012 | $0.00202 |
| Haiku 4.5 | $0.00006 | $0.00101 |
Grade A, and why
common-agent-guardrails 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 yesterday.
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 — 96 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Agent Guardrail Standard
Priority: P1 (HIGH)
A rule that must always hold belongs in a hook, not in a prompt. Prompts persuade; hooks decide.
1. What Belongs in a Guardrail
- Absolute compliance only: encode a rule here when a single violation is unacceptable, not when it is merely preferred.
- Deterministic check: the decision must be computable from tool name, arguments, and repo state — never from model judgment.
- Paired with a skill: the skill teaches the rule, the guardrail enforces it. Ship both or the rule decays.
- For unfamiliar workspaces, use the admission checklist; it is review guidance, not a sandbox or proof of enforcement.
2. Required Guardrail Classes
| Class | Trigger | Decision |
|---|---|---|
| Protected paths | edit to generated, vendored, or frozen files | block |
| Secret deny | edit or read of .env*, .ssh/, credentials*.json|yaml, identity files |
block |
| Test lock | test-file edit while a bug-fix workflow is active | block |
| Formatter | after any accepted edit | run, then report |
| Production action | deploy, migration, or destructive command against production | ask named owner |
| Scope fence | writes outside the declared task scope | ask |
3. Decision Semantics
- Exit 0: allow, stay silent. Reserve stdout for the formatter class.
- Exit 2: block. Print the rule violated and the sanctioned alternative on stderr, never a generic denial.
- Any other exit: ask a human. Use it when the check is inconclusive, not as a soft block.
- Fail closed on production classes: if the guardrail cannot evaluate, treat production actions as blocked.
4. Test Lock During Bug Fixes
- Write the failing test first; the agent proves the bug reproduces before touching production code.
- Lock every test path for the duration of the fix so the proof cannot be weakened into passing.
- Unlock only when the fix is verified, or when the operator states the test itself is the defect.
What ships with it
4 files 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.
- yesterday Changed · +2 lines ad093b172823
- 1mo ago First seen · 94 lines · 60 tokens per session scan A 066122da6f35
common-agent-guardrails is a skill published in the GitHub repository HoangNguyen0403/agent-skills-standard (582 stars, last pushed today), licensed MIT. It adds 60 tokens to every session and 1,008 once invoked, about $0.0002 per session on Opus 5.5. 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 2026-09-25.
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