SubagentStart

SubagentStart is a hook for Claude Code from smrafiz/claude-supercharger. Its token cost is not measured, scanned A, a copy of SessionStart, MIT.

A set of commands that runs when a helper agent starts work. A subagent is a separate agent working on part of a larger task.

In plain words
What is it for?
Useful for preparing subagents, checking whether they may proceed, and tracking their initial cost.
Why use it?
It applies safety, discovery, circuit-breaker, and cost checks at the start of each helper task.

Hook for Claude Code

Written for Claude Code: ${CLAUDE_PLUGIN_ROOT} variable. Also seen: mentions subagents.

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 supercharger plugin — 35 commands, 10 agents, 28 hooks shipped together

One of 28 entries in hooks.json upstream. Installing this one merges just its entry into your config; the other 27 are separate, each on its own page.

Good fit Useful for preparing subagents, checking whether they may proceed, and tracking their initial cost.

Compare 6 hooks from other repositories ↓
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 smrafiz/claude-supercharger
Claude Code
/plugin install supercharger

Made for: Claude Code.

Or install supercharger, the plugin that ships this one along with the rest of its 35 commands, 10 agents, 28 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/smrafiz/claude-supercharger/subagent-start.svg)](https://agentmods.dev/hooks/smrafiz/claude-supercharger/subagent-start)
Your own site
<a href="https://agentmods.dev/hooks/smrafiz/claude-supercharger/subagent-start"><img src="https://agentmods.dev/badge/hooks/smrafiz/claude-supercharger/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. A grade says what 26 rules found in the file — not that it is safe.
Origin 63% 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 8d 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

63% identical to SessionStart — 38 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 · 43 lines

What it actually says

{
  "SubagentStart": [
    {
      "hooks": [
        {
          "type": "command",
          "command": "\"${CLAUDE_PLUGIN_ROOT}\"/hooks/subagent-circuit-breaker.sh",
          "timeout": 15
        }
      ]
    },
    {
      "hooks": [
        {
          "type": "command",
          "command": "\"${CLAUDE_PLUGIN_ROOT}\"/hooks/subagent-discovery.sh",
          "async": true,
          "timeout": 120
        }
      ],
      "matcher": "*"
    },
    {
      "hooks": [
        {
          "type": "command",
          "command": "\"${CLAUDE_PLUGIN_ROOT}\"/hooks/subagent-safety.sh",
          "timeout": 15
        }
      ]
    },
    {
      "hooks": [
        {
          "type": "command",
          "command": "\"${CLAUDE_PLUGIN_ROOT}\"/hooks/subagent-cost.sh start",
          "async": true,
          "timeout": 120
        }
      ]
    }
  ]
}
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. 8d ago First seen · 43 lines scan A c1d58ffae43a

Subscribe to this mod's changes

SubagentStart is a hook published in the GitHub repository smrafiz/claude-supercharger (11 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. It is 63% identical to SessionStart, differing in 38 lines, and is treated as a copy.