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SessionStart

SessionStart is a hook for Claude Code from metraton/gaia. Its token cost is not measured, scanned A, a copy of PreToolUse, MIT.

A startup hook that runs a Python session-start script when an AI coding session starts, resumes, or is compacted. A hook is an automatic action triggered by a specified event.

In plain words
What is it for?
Use it to run session_start.py during startup, session resume, and context compaction.
Why use it?
It lets the project perform session setup automatically instead of relying on the agent or developer to run the script manually at each of those events.

Hook for Claude Code

Written for Claude Code: ${CLAUDE_PLUGIN_ROOT} variable.

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 gaia plugin — 39 skills, 9 agents, 12 hooks shipped together

One of 12 entries in hooks.json upstream. Installing this one merges just its entry into your config; the other 11 are separate, each on its own page.

not rated 4repo changed 10d ago A scan tokens not measured copy · 66% MIT

Good fit Use it to run session_start.py during startup, session resume, and context compaction.

Compare 6 hooks from other repositories ↓
View source ↗ metraton/gaia npmjs.com
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 metraton/gaia
Claude Code
/plugin install gaia

Made for: Claude Code.

Or install gaia, the plugin that ships this one along with the rest of its 39 skills, 9 agents, 12 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 SessionStart

README.md
[![agentmods](https://agentmods.dev/badge/hooks/metraton/gaia/session-start/github.svg)](https://agentmods.dev/hooks/metraton/gaia/session-start)
Your own site
<a href="https://agentmods.dev/hooks/metraton/gaia/session-start"><img src="https://agentmods.dev/badge/hooks/metraton/gaia/session-start/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.

agentmods 80×15 button for SessionStart

Your own site · 80×15
<a href="https://agentmods.dev/hooks/metraton/gaia/session-start"><img src="https://agentmods.dev/badge/hooks/metraton/gaia/session-start.svg" alt="Reviewed on agentmods" width="80" 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. A grade says what 26 rules found in the file — not that it is safe.
Origin 66% copy Near-identical to another mod in the catalogue.
Security

Grade A, and why

SessionStart 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 10d 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

66% identical to PreToolUse — 27 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.

hooks/hooks.json · 13 lines

What it actually says

{
  "SessionStart": [
    {
      "matcher": "startup|resume|clear|compact|fork",
      "hooks": [
        {
          "type": "command",
          "command": "sh \"${CLAUDE_PLUGIN_ROOT}/hooks/launch.sh\" \"${CLAUDE_PLUGIN_ROOT}/hooks/session_start.py\""
        }
      ]
    }
  ]
}
Same file

What 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.

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. 10d ago Changed a35dbe77d5f8
  2. 1mo ago First seen · 13 lines scan A 9462a28d1bee

Subscribe to this mod's changes

SessionStart is a hook published in the GitHub repository metraton/gaia (4 stars, last pushed 2d 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. It is 66% identical to PreToolUse, differing in 27 lines, and is treated as a copy.

Claude CodeDevOps and cloudOrchestrationSecurityai-agentsclaude-code-plugin
Related

Other hooks, from other repositories

PostToolUse

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

supabase/supabase · not measured

SessionStart

Runs when a session starts, executing on-start.js via node. From google-gemini/gemini-cli.

google-gemini/gemini-cli · not measured

SessionStart

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

supabase/supabase · not measured

PreToolUse

Runs before the agent uses a tool for Bash tool calls, running an inline shell check. From apache/superset.

apache/superset · not measured

PreToolUse

Runs before the agent uses a tool, executing pre-write.sh and pre-bash.sh (2 commands). From anthropics/claude-cookbooks.

anthropics/claude-cookbooks · not measured

SessionStart

Runs when a session starts, executing session-start.sh. From anthropics/claude-cookbooks.

anthropics/claude-cookbooks · not measured