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PreToolUse

PreToolUse is a hook for coding agents from nexus-substrate/nexus-agents. Its token cost is not measured, scanned A, original, MIT.

A pre-tool hook configuration that runs checks before selected agent actions. It blocks code pushes or pull-request merges when the fitness check fails and warns when sensitive files may contain credentials.

In plain words
What is it for?
Use it before Git pushes and pull-request merges to run the fitness gate, and before editing environment or credential files to run the secret scan.
Why use it?
It adds automated gates around two risky operations: releasing code and writing secrets. This can stop a low-quality change or flag accidental exposure before it reaches a repository.

Hook

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 nexus-agents plugin — 33 skills, 16 agents, 1 hook shipped together

not rated 18 today A scan tokens not measured original MIT
View the source file nexus-substrate/nexus-agents
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 nexus-substrate/nexus-agents
Claude Code
/plugin install nexus-agents

Or install nexus-agents, the plugin that ships this one along with the rest of its 33 skills, 16 agents, 1 hook.

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/nexus-substrate/nexus-agents/pre-tool-use.svg)](https://agentmods.dev/hooks/nexus-substrate/nexus-agents/pre-tool-use)
Your own site
<a href="https://agentmods.dev/hooks/nexus-substrate/nexus-agents/pre-tool-use"><img src="https://agentmods.dev/badge/hooks/nexus-substrate/nexus-agents/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 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 4d 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.

hooks/hooks.json · 20 lines

What it actually says

{
  "PreToolUse": [
    {
      "matcher": {
        "tool_name": "Bash",
        "tool_input": "git push|gh pr merge"
      },
      "command": "${CLAUDE_PLUGIN_ROOT}/hooks/fitness-gate.sh",
      "description": "Block push/merge if fitness score < 90 (#1830)"
    },
    {
      "matcher": {
        "tool_name": "Write|Edit",
        "tool_input": "\\.env|credentials\\.json|secrets\\.ya?ml"
      },
      "command": "${CLAUDE_PLUGIN_ROOT}/hooks/secret-scan.sh",
      "description": "Warn on credential patterns in sensitive files (#1830)"
    }
  ]
}
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. 4d ago First seen · 20 lines scan A 8340db7285b9

Subscribe to this mod's changes

PreToolUse is a hook published in the GitHub repository nexus-substrate/nexus-agents (18 stars, last pushed today), 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 2026-08-30.

Security
Related

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PostToolUse

Runs after a tool call finishes for Write and Edit tool calls, executing format_and_lint.sh. From supabase/supabase.

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Runs when a session starts on startup, executing install_pkgs.sh. From supabase/supabase.

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PreToolUse

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SessionStart

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anthropics/claude-cookbooks · not measured