What is SubagentStart?

An automatic command that runs when a task-verifier subagent starts. It invokes the cas tool's SubagentStart hook.

Use it to run follow-up actions at the start of task-verifier subagents, as defined by the cas hook.

It allows a predefined check or setup action to happen whenever that specific kind of helper process begins.

SubagentStart — Hook by codingagentsystem

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/codingagentsystem/cas/subagent-start

Clone the repo

git clone --depth 1 https://github.com/codingagentsystem/cas

Made for: Claude Code.

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 original No closer match found 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 yesterday.

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.

.claude/settings.json · 15 lines

What it actually says

{
  "SubagentStart": [
    {
      "hooks": [
        {
          "async": true,
          "command": "cas hook SubagentStart",
          "timeout": 2000,
          "type": "command"
        }
      ],
      "matcher": "task-verifier"
    }
  ]
}

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.

yesterday First seen · 15 lines scan A 52f693d89dd1

Subscribe to this mod's changes

SubagentStart is a hook published in the GitHub repository codingagentsystem/cas (151 stars, last pushed 5mo 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. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

Building agents Planning ai ai-orchestration claude cli coding-assistant mcp

SubagentStart

Getting it into your agent

Grade A, and why

Nothing flagged

What it actually says

What this file has done since we first saw it

Other hooks, from other repositories

PreToolUse

SubagentStart

SubagentStop

SubagentStop

SubagentStop

SubagentStop