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.
/plugin marketplace add metraton/gaia/plugin install gaiaWrote 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.
[](https://agentmods.dev/hooks/metraton/gaia/pre-tool-use)<a href="https://agentmods.dev/hooks/metraton/gaia/pre-tool-use"><img src="https://agentmods.dev/badge/hooks/metraton/gaia/pre-tool-use/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/hooks/metraton/gaia/pre-tool-use"><img src="https://agentmods.dev/badge/hooks/metraton/gaia/pre-tool-use.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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 15d 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.
How it starts
The opening of the file, as written. The whole thing — 64 lines — stays where its author put it; the contents beside it link to each section on GitHub.
{
"PreToolUse": [
{
"matcher": "Task",
"hooks": [
{
"type": "command",
"command": "sh \"${CLAUDE_PLUGIN_ROOT}/hooks/launch.sh\" \"${CLAUDE_PLUGIN_ROOT}/hooks/pre_tool_use.py\"",
"onFailure": "block"
}
]
},
{
"matcher": "Agent",
"hooks": [
{
"type": "command",
"command": "sh \"${CLAUDE_PLUGIN_ROOT}/hooks/launch.sh\" \"${CLAUDE_PLUGIN_ROOT}/hooks/pre_tool_use.py\"",
"onFailure": "block"
}
]
},
{
"matcher": "SendMessage",
"hooks": [
{
"type": "command",
"command": "sh \"${CLAUDE_PLUGIN_ROOT}/hooks/launch.sh\" \"${CLAUDE_PLUGIN_ROOT}/hooks/pre_tool_use.py\"",
"onFailure": "block"
}
]
},
{
"matcher": "AskUserQuestion",
"hooks": [
{
"type": "command",
"command": "sh \"${CLAUDE_PLUGIN_ROOT}/hooks/launch.sh\" \"${CLAUDE_PLUGIN_ROOT}/hooks/pre_tool_use.py\"",
"onFailure": "block"
}
]
},
{
"matcher": "Read|Edit|Write|Glob|Grep|WebSearch|WebFetch|NotebookEdit",
"hooks": [
{
"type": "command",
"command": "sh \"${CLAUDE_PLUGIN_ROOT}/hooks/launch.sh\" \"${CLAUDE_PLUGIN_ROOT}/hooks/pre_tool_use.py\"",
"onFailure": "block"
}
]
},
{
"matcher": "^(?!Agent$)(?!Artifact$)(?!AskUserQuestion$)(?!CronCreate$)(?!CronDelete$)(?!CronList$)(?!Edit$)(?!EndConversation$)(?!EnterPlanMode$)(?!EnterWorktree$)(?!ExitPlanMode$)(?!ExitWorktree$)(?!Glob$)(?!Grep$)(?!ListAgents$)(?!ListMcpResourcesTool$)(?!LSP$)(?!NotebookEdit$)(?!PushNotification$)(?!Read$)(?!ReadMcpResourceTool$)(?!ReportFindings$)(?!ScheduleWakeup$)(?!SendFeedback$)(?!SendMessage$)(?!SendUserFile$)(?!ShareOnboardingGuide$)(?!Skill$)(?!SubagentHandback$)(?!Task$)(?!TaskCreate$)(?!TaskGet$)(?!TaskList$)(?!TaskOutput$)(?!TaskStop$)(?!TaskUpdate$)(?!TodoWrite$)(?!ToolSearWhat else hooks.json configures
This page is one entry in a file that holds 12. Installing the file brings all of them; each is measured and scanned on its own page.
- Hook PostCompact A not measured
- Hook PostToolUse A not measured
- Hook PostToolUseFailure A not measured
- Hook PreCompact A not measured
- Hook SessionEnd A not measured
- Hook SessionStart A not measured
- Hook Stop A not measured
- Hook SubagentStart A not measured
- Hook SubagentStop A not measured
- Hook TaskCompleted A not measured
- Hook UserPromptSubmit A not measured
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.
- 15d ago Changed · +6 lines 2f46b6ae3196
- 23d ago Changed 2f5788d7f545
- 1mo ago Changed · +9 lines aa9774b5d473
- 2mo ago First seen · 49 lines scan A ead6d8a1183c
PreToolUse is a hook published in the GitHub repository metraton/gaia (4 stars, last pushed yesterday), 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 2026-08-31.
Other hooks, from other repositories
SessionStart
Runs when a session starts on startup, executing install_pkgs.sh. From supabase/supabase.
PostToolUse
Runs after a tool call finishes for Write and Edit tool calls, executing format_and_lint.sh. From supabase/supabase.
SessionStart
Runs when a session starts, executing on-start.js via node. From google-gemini/gemini-cli.
PreToolUse
Runs before the agent uses a tool for Bash tool calls, running an inline shell check. From apache/superset.
PreToolUse
Runs before the agent uses a tool, executing pre-write.sh and pre-bash.sh (2 commands). From anthropics/claude-cookbooks.
PostToolUse
Runs after a tool call finishes for Bash tool calls, executing hooks.sh via sh (3 commands). From anthropics/claude-plugins-official.