AskUserQuestion tool doesn't render interactive UI — returns empty response immediately

[petter-b]

Description

The AskUserQuestion tool does not render any interactive UI (question text, selectable options). Instead, it immediately returns with "User answered Claude's questions:" and an empty/blank answer, skipping the interactive selection entirely.

Steps to Reproduce

1. Start a Claude Code session
2. Ask Claude to use the AskUserQuestion tool (e.g., "Can you ask me something?")
3. Claude calls AskUserQuestion with a question and multiple options
4. Expected: An interactive UI appears showing the question and selectable options
5. Actual: No UI is shown. The tool immediately returns with an empty response

Observed Behavior

The conversation flow looks like this:

> Can you ask me something, I want to check if the ask-user-question tool works

● Sure, let me test for you.

● User answered Claude's questions:
  (empty)

● The AskUserQuestion tool is working. It presented you with the question...

The question and options are never displayed. The tool returns as if the user answered, but with no content.

Environment

• Claude Code version: 2.1.63
• Platform: macOS (Darwin 25.3.0, Apple M4)
• Shell: zsh

Additional Context

A screenshot is available showing the exact behavior — will be added as a follow-up comment.

[petter-b]

[MickaelV0]

same issue here ! #29547

But only in a context of a /skill

[monsterhxw]

I have the same issue.

[terrylica]

Root Cause Found + Fix

I tracked this down to a PreToolUse hook with a wildcard matcher (*) returning updatedInput for ALL tools, which silently corrupts the AskUserQuestion input schema.

The Problem

When a PreToolUse hook returns updatedInput in its response, Claude Code replaces the tool's entire input with that object. If the hook injects extra properties (like env) into updatedInput for every tool call, it corrupts tools whose schema doesn't expect those properties.

For AskUserQuestion, the expected input is:

{"questions": [{"question": "...", "options": [...]}]}

But the hook was producing:

{"questions": [{"question": "...", "options": [...]}], "env": {"TERM": "dumb", "NO_PAGER": "1", ...}}

The extra env key causes the interactive UI to not render — the tool returns immediately with empty answers.

Minimal Reproduction

Any PreToolUse hook with:

1. matcher: "" (empty string = matches all tools), and
2. Returns updatedInput with injected properties (even if the properties are unrelated to the tool)

...will break AskUserQuestion, TaskCreate, and other UI tools.

The Fix (Hook Authors)

Never return updatedInput for tools that don't need input mutation. Use a passthrough allowlist:

const PASSTHROUGH_TOOLS = new Set([
  "AskUserQuestion", "EnterPlanMode", "ExitPlanMode",
  "TaskCreate", "TaskUpdate", "TaskList", "TaskGet",
  "Read", "Glob", "Grep", "WebSearch", "WebFetch",
  "Agent", "Skill",
]);

async function main() {
  const input = parseStdin();
  
  // UI/metadata tools: allow without mutation
  if (PASSTHROUGH_TOOLS.has(input.tool_name)) {
    console.log(JSON.stringify({
      hookSpecificOutput: {
        hookEventName: "PreToolUse",
        permissionDecision: "allow"
      }
    }));
    return;
  }

  // Only mutate tools that actually need it (e.g., Bash)
  // ...
}

Suggestion for Claude Code Team

Claude Code should strip unknown properties from updatedInput before applying it, using each tool's schema as a filter. This would make hooks forward-compatible and prevent this class of bugs entirely. Alternatively, validate that updatedInput only contains keys present in the tool's parameter schema, and warn/ignore extras.

Fix Applied

I've published the fix in terrylica/cc-skills v11.63.1 — the pretooluse-subprocess-stdin-inlet-guard.ts hook now uses a PASSTHROUGH_TOOLS set to skip UI tools entirely.

Related closed issues: #13439, #10400

[petter-b]

Downgrading to 2.1.62 ia another "fix".

[monsterhxw]

My Workaround: Remove AskUserQuestion from the skill's allowed-tools frontmatter. The tool then works normally under default permissions.

[petter-b]

My Workaround: Remove AskUserQuestion from the skill's allowed-tools frontmatter. The tool then works normally under default permissions.

It's not just a problem with skills. AskUserQuestion does not work at all.