SubagentStart

SubagentStart is a hook for Claude Code from tettethu/VibeGame. Its token cost is not measured, scanned A, a copy of SessionEnd, Apache-2.0.

A startup hook that runs a Python script whenever a subagent begins. A subagent is a separate coding-agent worker handling part of a larger task.

In plain words
What is it for?
Use it to send a web notification or trigger other project-specific actions when a Claude subagent starts.
Why use it?
It lets a project react automatically when a worker starts, without requiring a manual command.

Hook for Claude Code

One of 10 entries in settings.json — they are configured in one file and arrive together.

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/tettethu/vibegame/subagent-start
Clone the repo
git clone --depth 1 https://github.com/tettethu/VibeGame

Made for: Claude Code.

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 SubagentStart

README.md
[![agentmods](https://agentmods.dev/badge/hooks/tettethu/vibegame/subagent-start.svg)](https://agentmods.dev/hooks/tettethu/vibegame/subagent-start)
Your own site
<a href="https://agentmods.dev/hooks/tettethu/vibegame/subagent-start"><img src="https://agentmods.dev/badge/hooks/tettethu/vibegame/subagent-start.svg" alt="Measured on agentmods" 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. Scan, not verified.
Origin 89% copy Near-identical to another mod in the catalogue.
Security

Grade A, and why

SubagentStart 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 5d 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

89% identical to SessionEnd — 4 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.

src/.claude/settings.json · 14 lines

What it actually says

{
  "SubagentStart": [
    {
      "matcher": "",
      "hooks": [
        {
          "type": "command",
          "command": "python3 \"$CLAUDE_PROJECT_DIR/.vibegame/hooks/web_hook.py\" --source-app claude --event-type SubagentStart",
          "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. 5d ago First seen · 14 lines scan A a95abba35403

Subscribe to this mod's changes

SubagentStart is a hook published in the GitHub repository tettethu/VibeGame (200 stars, last pushed 6d 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 89% identical to SessionEnd, differing in 4 lines, and is treated as a copy.