A pair of hooks that run before the agent uses any tool: one checks tool safety and the other collects information. Hooks are automatic actions attached to agent events.

Use it to inspect tool calls with guard-hook.js and collect related data with collector-hook.js.

It adds a safety check and records tool activity before actions begin.

PreToolUse — Hook by core0-io

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/core0-io/nio/pre-tool-use

Clone the repo

git clone --depth 1 https://github.com/core0-io/nio

Or install nio, the plugin that ships this one along with the rest of its 7 skills, 8 hooks.

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 53% 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

53% identical to SessionStart — 16 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/claude-code/hooks/hooks.json · 21 lines

What it actually says

{
  "PreToolUse": [
    {
      "matcher": ".*",
      "hooks": [
        {
          "type": "command",
          "command": "node \"${CLAUDE_PLUGIN_ROOT}/skills/nio/scripts/guard-hook.js\"",
          "timeout": 10,
          "statusMessage": "Nio: checking tool safety..."
        },
        {
          "type": "command",
          "command": "node \"${CLAUDE_PLUGIN_ROOT}/skills/nio/scripts/collector-hook.js\"",
          "timeout": 10,
          "async": true
        }
      ]
    }
  ]
}

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 · 21 lines scan A a9f9a16cc669

Subscribe to this mod's changes

PreToolUse is a hook published in the GitHub repository core0-io/nio (19 stars, last pushed 12d 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 53% identical to SessionStart, differing in 16 lines, and is treated as a copy.

AI Safety Autonomous Agents agent-guard agentic-ai ai-agent ai-governance

PreToolUse

Getting it into your agent

Grade A, and why

Nothing flagged

This is a copy

What it actually says

What this file has done since we first saw it

Other hooks, from other repositories

SessionStart

PreToolUse

InstructionsLoaded

SessionEnd

PostToolUse

PostToolUse