PreToolUse

A pre-tool hook that runs a small shell check before Stuart's MCP tools or web-fetching tools are used. A hook is an automatic action triggered by another action.

In plain words
What is it for?
It applies to calls matching Stuart's MCP servers and to WebFetch calls, returning an allow decision and its reason.
Why use it?
It automatically marks those read-only operations as allowed, reducing permission prompts for the specified tools.

Hook

Install

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.

agentmods
npx agentmods add hooks/yrebrac/stuart/pre-tool-use
Clone the repo
git clone --depth 1 https://github.com/yrebrac/stuart
Per session not measured What this adds to a session before it is invoked.
When invoked not measured Not applicable: nothing here is loaded into a session.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Security

Grade A, and why

PreToolUse 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 commands this hook runs, not an audit. A hook is shell that executes on your machine at the event it names, which is why every command in it is printed with what was found.

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.

hooks/hooks.json · 22 lines

What it actually says

{
  "PreToolUse": [
    {
      "matcher": "mcp__plugin_stuart_.*",
      "hooks": [
        {
          "type": "command",
          "command": "echo '{\"hookSpecificOutput\":{\"hookEventName\":\"PreToolUse\",\"permissionDecision\":\"allow\",\"permissionDecisionReason\":\"Stuart MCP tool — read-only, auto-approved by plugin\"}}'"
        }
      ]
    },
    {
      "matcher": "WebFetch",
      "hooks": [
        {
          "type": "command",
          "command": "echo '{\"hookSpecificOutput\":{\"hookEventName\":\"PreToolUse\",\"permissionDecision\":\"allow\",\"permissionDecisionReason\":\"Web fetch — read-only, auto-approved by plugin\"}}'"
        }
      ]
    }
  ]
}
Changes

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.

  1. yesterday First seen · 22 lines scan A 712bb4d77a77

Subscribe to this mod's changes

PreToolUse is a hook published in the GitHub repository yrebrac/stuart (1 stars, last pushed 5mo ago), licensed MIT. Its token cost is not measured: a hook is shell that never enters the context. 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 2026-08-31.