agentmods.dev

PreToolUse

A pre-action security check that runs before an agent uses shell commands, web access, file editing, notebooks, or connected tools. It invokes Skarn Guard in audit mode.

In plain words
What is it for?
Use it to monitor agent actions before Bash, web, writing, editing, notebook, and MCP tool calls.
Why use it?
It creates an audit record before potentially sensitive or changing actions take place, so tool use can be inspected against security rules.

Hook

Part of the skarn-guard plugin — 6 hooks, 1 MCP server shipped together

31 6d ago A scan tokens not measured original MIT
View the source file skarn-security/agent-guard
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/skarn-security/agent-guard/pre-tool-use
Clone the repo
git clone --depth 1 https://github.com/skarn-security/agent-guard

Or install skarn-guard, the plugin that ships this one along with the rest of its 6 hooks, 1 MCP server.

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 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.

claude/hooks/hooks.json · 14 lines

What it actually says

{
  "PreToolUse": [
    {
      "matcher": "Bash|WebFetch|WebSearch|Write|Edit|MultiEdit|NotebookEdit|mcp__.*",
      "hooks": [
        {
          "type": "command",
          "command": "skarn guard --guard-mode audit",
          "timeout": 5
        }
      ]
    }
  ]
}
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. 3d ago First seen · 14 lines scan A 9585cf6b067c

Subscribe to this mod's changes

PreToolUse is a hook published in the GitHub repository skarn-security/agent-guard (31 stars, last pushed 6d 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 2026-08-30.

gemini-cli-extension
Related

Other hooks, from other repositories

BeforeTool

Runs on the BeforeTool event for tool == "run_shell_command", tool == "run_shell_command", tool == "run_shell_command" && tool_input.command matches "^\\s*(npm (install, test, i, ci), pnpm (install, test, i), yarn (install, test, add, remove, upgrade), bun (install, test, i, add, remove), cargo build, make, docker…

Jamkris/everything-gemini-code · not measured

SessionStart

Runs when a session starts, executing run.js via node. From Jamkris/everything-gemini-code.

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PreCompact

Runs before the context is compacted, executing nmem-hook-save.py with --event. From nowledge-co/community.

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SessionEnd

Runs when a session ends, executing nmem-hook-save.py with --event and --detach. From nowledge-co/community.

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SessionStart

Runs when a session starts, executing session-start.py via python3. From tractorjuice/arckit-gemini.

tractorjuice/arckit-gemini · not measured

BeforeTool

Runs on the BeforeTool event for ^(mcp_.*, .*(http, web, search, fetch, request, api, connect).*, Read, Write, Edit, MultiEdit, NotebookEdit, Bash, Grep and Glob)$ tool calls, running python -m securedact_enforced.gemini_hook --event BeforeTool. From GigantesHJI/securedact-mcp.

GigantesHJI/securedact-mcp · not measured