What is SessionStart?

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.

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

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.

SessionStart — Hook by metraton

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/metraton/gaia/session-start

Clone the repo

git clone --depth 1 https://github.com/metraton/gaia

Or install gaia, the plugin that ships this one along with the rest of its 38 skills, 9 agents, 11 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 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 2d 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|compact",
      "hooks": [
        {
          "type": "command",
          "command": "python3 ${CLAUDE_PLUGIN_ROOT}/hooks/session_start.py"
        }
      ]
    }
  ]
}

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.

2d 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 (3 stars, last pushed 5d 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.

Orchestration ai-agents claude-code claude-code-plugin

SessionStart

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

Stop

PreToolUse

PostToolUseFailure

PostToolUse

Stop

PostToolUse