SubagentStart

SubagentStart is a hook for coding agents from tellang/triflux. Its token cost is not measured, scanned A, a copy of SessionStart, MIT.

A startup hook that runs a Node.js command whenever a subagent begins. A subagent is a helper agent working on part of a larger task.

In plain words
What is it for?
Use it to trigger shared setup or orchestration logic when subagents start, provided the required hook file can be found.
Why use it?
It lets the configured hook orchestrator run automatically at the start of each helper-agent session.

Hook

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 triflux plugin — 29 skills, 1 agent, 12 hooks shipped together

One of 12 entries in hooks.json — they are configured in one file and arrive together.

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 tellang/triflux
Claude Code
/plugin install triflux

Or install triflux, the plugin that ships this one along with the rest of its 29 skills, 1 agent, 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 SubagentStart

README.md
[![agentmods](https://agentmods.dev/badge/hooks/tellang/triflux/subagent-start.svg)](https://agentmods.dev/hooks/tellang/triflux/subagent-start)
Your own site
<a href="https://agentmods.dev/hooks/tellang/triflux/subagent-start"><img src="https://agentmods.dev/badge/hooks/tellang/triflux/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 1 finding. Scan, not verified.
Origin 94% copy Near-identical to another mod in the catalogue.
Security

Grade A, and why

SubagentStart scanned grade A with 1 finding 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 4d 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.

Runs shell commandslowCapability

Expected in a hook, worth knowing in a rule or an instructions file.

"command": "node -e \"const fs=require('node:fs'),os=require('node:os'),path=require('node:path'),cp=require('node:child_process');const roots=[];try{roots.push(fs.readFileSync(path.join(os.homedir(),'.claude','scripts',
Origin

This is a copy

94% identical to SessionStart — 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.

hooks/hooks.json · 14 lines

What it actually says

{
  "SubagentStart": [
    {
      "matcher": "*",
      "hooks": [
        {
          "type": "command",
          "command": "node -e \"const fs=require('node:fs'),os=require('node:os'),path=require('node:path'),cp=require('node:child_process');const roots=[];try{roots.push(fs.readFileSync(path.join(os.homedir(),'.claude','scripts','.tfx-pkg-root'),'utf8').trim())}catch{}roots.push(process.env.PLUGIN_ROOT,process.env.CLAUDE_PLUGIN_ROOT);try{roots.push(cp.execFileSync('git',['rev-parse','--show-toplevel'],{encoding:'utf8',stdio:['ignore','pipe','ignore']}).trim())}catch{}roots.push(process.cwd());const root=roots.find(r=>r&&fs.existsSync(path.join(r,'hooks','hook-orchestrator.mjs')));if(!root){console.error('[triflux hook] cannot locate hooks/hook-orchestrator.mjs');process.exit(1)}const child=cp.spawnSync(process.execPath,[path.join(root,'hooks','hook-orchestrator.mjs')],{stdio:'inherit',env:process.env,windowsHide:true});process.exit(child.status??(child.signal?1:0));\"",
          "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. 4d ago First seen · 14 lines scan A 1a6a973213b5

Subscribe to this mod's changes

SubagentStart is a hook published in the GitHub repository tellang/triflux (7 stars, last pushed 13d 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 1 finding (runs shell commands). It is 94% identical to SessionStart, differing in 4 lines, and is treated as a copy.