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PreToolUse

PreToolUse is a hook for Claude Code from FreePeak/LeanKG. Its token cost is not measured, scanned A, a copy of SessionStart, Apache-2.0.

A hook that runs before the agent uses a tool.

In plain words
What is it for?
Use it to run the LeanKG pre-tool-use script before every tool call.
Why use it?
It enables LeanKG to process or prepare context before tool activity begins.

Hook for Claude Code

Runs only inside its plugin — its command needs a path that Claude Code sets for a plugin’s own hooks and for nothing else. Install the plugin, not this.

Part of the LeanKG plugin — 2 skills, 1 command, 2 agents, 2 hooks shipped together

One of 2 entries in hooks.json — they are configured in one file and arrive together.

not rated 215 11d ago A scan tokens not measured copy · 52% Apache-2.0
View the source file FreePeak/LeanKG
Install

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.

Claude Code
/plugin marketplace add FreePeak/LeanKG
Claude Code
/plugin install LeanKG

Made for: Claude Code.

Or install LeanKG, the plugin that ships this one along with the rest of its 2 skills, 1 command, 2 agents, 2 hooks.

Wrote 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.

agentmods badge for PreToolUse

README.md
[![agentmods](https://agentmods.dev/badge/hooks/freepeak/leankg/pre-tool-use.svg)](https://agentmods.dev/hooks/freepeak/leankg/pre-tool-use)
Your own site
<a href="https://agentmods.dev/hooks/freepeak/leankg/pre-tool-use"><img src="https://agentmods.dev/badge/hooks/freepeak/leankg/pre-tool-use.svg" alt="Measured on agentmods" height="20"></a>
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 52% 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 5d 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

52% identical to SessionStart — 8 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.

.claude-plugin/hooks/hooks.json · 13 lines

What it actually says

{
  "PreToolUse": [
    {
      "matcher": "*",
      "hooks": [
        {
          "type": "command",
          "command": "node \"${CLAUDE_PLUGIN_ROOT}/hooks/leankg-pretooluse.mjs\""
        }
      ]
    }
  ]
}
Same file

What else hooks.json configures

This page is one entry in a file that holds 2. Installing the file brings all of them; each is measured and scanned on its own page.

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. 5d ago First seen · 13 lines scan A e3b575890050

Subscribe to this mod's changes

PreToolUse is a hook published in the GitHub repository FreePeak/LeanKG (215 stars, last pushed 11d ago), licensed Apache-2.0. 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 52% identical to SessionStart, differing in 8 lines, and is treated as a copy.

concise-contextgraph-databaseknowledge-graphlean-codelean-contextmcp
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