A set of pre-tool checks that runs before an agent writes files, edits code, executes shell commands, or uses selected search and filesystem tools. The checks include gates for secrets, scope, project state, and framework choices.

Use it to enforce project and security checks before file edits, commands, web searches, or filesystem changes.

It adds safeguards before changes or potentially sensitive actions are made. This can prevent accidental secret exposure, unapproved scope changes, and workflow violations.

PreToolUse — Hook by haabe

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/haabe/mycelium/pre-tool-use

Clone the repo

git clone --depth 1 https://github.com/haabe/mycelium

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 59% copy Near-identical to another mod 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 3d ago.

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.

Origin

This is a copy

59% identical to SessionStart — 99 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

plugins/mycelium/hooks/hooks.json · 104 lines

How it starts

The opening of the file, as written. The whole thing — 104 lines — stays where its author put it; the contents beside it link to each section on GitHub.

{
  "PreToolUse": [
    {
      "matcher": "Write|Edit|MultiEdit",
      "hooks": [
        {
          "type": "command",
          "command": "bash ${CLAUDE_PLUGIN_ROOT}/hooks/gate.sh",
          "timeout": 5,
          "statusMessage": "Mycelium preflight gate + secret scan"
        },
        {
          "type": "command",
          "command": "bash ${CLAUDE_PLUGIN_ROOT}/hooks/discovery-gate.sh",
          "timeout": 5,
          "statusMessage": "Mycelium discovery gate (new source files in discovery-untouched projects)"
        },
        {
          "type": "command",
          "command": "bash ${CLAUDE_PLUGIN_ROOT}/hooks/brownfield-gate.sh",
          "timeout": 5,
          "statusMessage": "Mycelium brownfield gate (one-shot: existing code, no discovery state)"
        },
        {
          "type": "command",
          "command": "bash ${CLAUDE_PLUGIN_ROOT}/hooks/scope-gate.sh",
          "timeout": 5,
          "statusMessage": "Mycelium scope enforcement"
        },
        {
          "type": "command",
          "command": "bash ${CLAUDE_PLUGIN_ROOT}/hooks/framework-guard.sh",
          "timeout": 5,
          "statusMessage": "Mycelium framework-guard (dogfood-mode only)"
        },
        {
          "type": "command",
          "command": "bash ${CLAUDE_PLUGIN_ROOT}/hooks/autonomous-evidence-guard.sh",
          "timeout": 5,
          "statusMessage": "Mycelium autonomous-evidence-guard (autonomous-mode only)"
        },
        {
          "type": "command",
          "command": "bash ${CLAUDE_PLUGIN_ROOT}/hooks/absence-claim-guard.sh"
        },
        {
          "type": "command",
          "command": "bash ${CLAUDE_PLUGIN_ROOT}/hooks/correction-attribution-guard.sh"
        }
      ]
    },
    {
      "matcher": "Bash",
      "hooks": [
        {
          "type": "command",
          "command": "bash ${CLAUDE_PLUGIN_ROOT}/hooks/framework-guard.sh",
          "timeout": 5,
          "statusMessage": "Mycelium framework-guard (Bash — dogfoo

Read the full file on GitHub · 104 lines

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.

3d ago First seen · 104 lines scan A 33904f76542a

Subscribe to this mod's changes

PreToolUse is a hook published in the GitHub repository haabe/mycelium (45 stars, last pushed 3d 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. It is 59% identical to SessionStart, differing in 99 lines, and is treated as a copy.

Security ai-agent claude-code delivery discovery product-development

PreToolUse

Getting it into your agent

Grade A, and why

Nothing flagged

This is a copy

How it starts

What this file has done since we first saw it

Other hooks, from other repositories

SessionStart

SubagentStop

Stop

PostToolUse

PreToolUse

UserPromptSubmit