Getting it into your agent
This one installs as part of its plugin. Adding the marketplace and installing the plugin brings it with everything else the plugin ships.
/plugin marketplace add yeaight7/agent-powerups/plugin install security-guardrailsWrote 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/yeaight7/agent-powerups/filesystem-mcp-guardrails)<a href="https://agentmods.dev/skills/yeaight7/agent-powerups/filesystem-mcp-guardrails"><img src="https://agentmods.dev/badge/skills/yeaight7/agent-powerups/filesystem-mcp-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/yeaight7/agent-powerups/filesystem-mcp-guardrails"><img src="https://agentmods.dev/badge/skills/yeaight7/agent-powerups/filesystem-mcp-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 | $0.00032 | $0.00692 |
| Opus 5.5 | $0.00013 | $0.00277 |
| Sonnet 5.5 | $0.00006 | $0.00138 |
| Haiku 4.5 | $0.00003 | $0.00069 |
Grade A, and why
filesystem-mcp-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 1mo 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 — 68 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Filesystem MCP Guardrails
When to use
Use when configuring, reviewing, or debugging a local filesystem MCP server — particularly when deciding which paths to expose, which methods to allow, and how to enforce workspace boundaries.
Safety Model
The core constraint is strict path bounding: the MCP server must only operate within explicitly declared workspace roots. No exceptions.
| Principle | Rule |
|---|---|
| Scope | Bind to the project workspace directory only — never /, ~, or OS dirs |
| Access | Start read-only; add write methods only when the use case requires them |
| Methods | Use an allowlist — block delete/move/rename by default |
| Secrets | Never expose .env, credential files, SSH keys, or token stores |
| Approval | Always require user approval before starting a new MCP server process |
Configuration Checklist
Before starting a filesystem MCP server:
- Allowed roots list is explicit and scoped to the project directory.
- No root is set to
/,~, or any system-level path. - Method allowlist is defined (e.g.,
read_file,list_directory,search_files). - Destructive methods (
delete_file,move_file,write_file) are explicitly enabled only if required. - Sensitive file patterns are excluded:
*.env,*.key,*.pem,*secrets*,.ssh/. - Server timeout is set (avoid hanging processes).
- Log output does not include file contents — only paths and operation results.
Workflow
- Define scope — identify which directories the agent legitimately needs to access for this task.
- Set roots — configure the server with the narrowest possible root list (usually just the project root).
- Define allowlist — start with read-only methods; add write methods only after explicit use-case review.
- Validate path boundaries — test that requests for paths outside the declared roots are refused with a clear error.
- Verify cleanup — confirm the server process exits cleanly when the session ends; no background processes left running.
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.
- 1mo ago First seen · 68 lines · 32 tokens per session scan A b8e0e9269349
filesystem-mcp-guardrails is a skill published in the GitHub repository yeaight7/agent-powerups (6 stars, last pushed 19d ago), licensed Apache-2.0. It adds 32 tokens to every session and 692 once invoked, about $0.0001 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 2026-09-14.
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