claude-code - 💡(How to fix) Fix PostToolUse agent hook fails with "Messages are required for agent hooks. This is a bug." [2 comments, 3 participants]

TL;DR

The PostToolUse hook with an agent type may require a "messages" field instead of or in addition to the "prompt" field to run successfully.

Guidance

• Verify the documentation for agent hooks to confirm the required fields, as there might be a discrepancy between the documented "prompt" field and the runtime error referencing "messages".
• Check if adding a "messages" field to the hook configuration resolves the issue, potentially wrapping the "prompt" string into an array.
• Test the hook with both "prompt" and "messages" fields to see if one or both are necessary for successful execution.
• Consider reporting the discrepancy between the documentation and the runtime error as a bug to ensure clarity for future users.

Example

"hooks": {
  "PostToolUse": [
    {
      "matcher": "Bash",
      "hooks": [
        {
          "type": "agent",
          "if": "Bash(gh pr create*)",
          "prompt": "A pull request was just created. Extract the PR URL from the command's stdout and post it to Slack via the slack_send_message MCP tool.",
          "messages": ["A pull request was just created. Extract the PR URL from the command's stdout and post it to Slack via the slack_send_message MCP tool."],
          "timeout": 90,
          "statusMessage": "Posting PR to Slack"
        }
      ]
    }
  ]
}

Notes

The solution assumes that the error message indicating a requirement for "messages" is accurate and that the documentation might be outdated or incorrect regarding the "prompt" field for agent hooks.

Recommendation

Apply workaround: Add a "messages" field to the hook configuration, as shown in the example, to potentially resolve the issue until the documentation discrepancy is addressed.