Configure an async hook

Add "async": true to a command hook's configuration to run it in the background without blocking Claude. This field is only available on type: "command" hooks.

This hook runs a test script after every Write tool call. Claude continues working immediately while run-tests.sh executes. When the script finishes, its output is delivered on the next conversation turn:

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Write",
        "hooks": [
          {
            "type": "command",
            "command": "/path/to/run-tests.sh",
            "async": true
          }
        ]
      }
    ]
  }
}

Once an async hook is running in the background, Claude Code doesn't enforce timeout on it. Claude Code still enforces timeout on a hook you run with asyncRewake.

Claude Code delivers an async hook's results only while the session runs:

• In non-interactive mode with the -p flag, Claude Code kills any async hook still running at teardown and finalizes it with outcome cancelled
• If your hook's work must outlive a claude -p session, start a fully detached process from it