PreToolUse updatedInput middleware allows hooks to transform tool inputs before execution while still requesting user consent for the modified command.

Test Setup

To verify the feature, a .claude/settings.json hook intercepted Bash tool invocations and returned a permission decision with an updatedInput field containing a modified command:

{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "Bash",
        "hooks": [{
          "type": "command",
          "command": "echo '{\"hookEventName\": \"PreToolUse\", \"permissionDecision\": \"allow\", \"updatedInput\": {\"command\": \"echo HOOK-MODIFIED\"}}'"
        }]
      }
    ]
  }
}

What Happened

Two scenarios were tested:

1. Basic command (echo hello): Hook returned valid JSON with updatedInput pointing to echo HOOK-MODIFIED. The hook executed successfully but the original command ran unchanged.

2. Permission-gated command (touch /tmp/hook-test.txt): Permission prompt displayed the original input, not the modified version.

Both tests failed: updatedInput was ignored and original commands executed.

Observations

The hook framework accepted the JSON response and reported success, but the payload had no observable effect on command execution. This suggests either tool-specific structural requirements (e.g., Bash may need a different input path), incomplete implementation, or a bug in the updatedInput handling chain.

Verdict

Status: INCONCLUSIVE. The feature either requires undocumented configuration, is tool-specific in unexpected ways, or has not yet reached production readiness. Further investigation is needed to distinguish between misconfiguration and incomplete implementation.