catalog / tool-constraints

ask_user_input_v0 enforces a 3-question, 4-option ceiling

verified

ask_user_input_v0 on Claude.ai enforces a schema-level ceiling of 3 questions and 4 options per question; exceeding either limit fails with a validation error.

  • Category: tool-constraints
  • Applies to: Claude.ai ✅ | Claude Code ❌ (tool doesn't exist) | Claude Desktop ❌ (tool doesn't exist)
  • Verified on: Claude.ai web, 2026-05-17
  • Verification tier: verified
  • Severity: Hard error

Symptom

A skill written for Claude.ai that calls ask_user_input_v0 with more than 3 questions, or with more than 4 options per question, fails with a schema validation error. The constraint isn't documented in user-facing skill-authoring guidance.

Cause

The tool's schema declares maxItems: 3 on the questions array and maxItems: 4 on the options array. The tool description mentions these limits in prose ("one question where possible — three is a ceiling, not a target", "2-4 short, mutually exclusive options") but they read as guidance rather than hard limits.

Reproduction

Reproduced 2026-05-17 on Claude.ai web: ask_user_input_v0 with 4 questions → schema validation error.

Fix

Cap questions at 3, options at 4. If elicitation needs more, chain across turns or use multi_select to combine. A portable skill that also targets Code/Desktop's AskUserQuestion (which caps at 4 questions) must conform to the stricter limit of 3.

Notes

Related Claude.ai hard ceilings: see image-search-result-count-bounds.md and recent-chats-max-n.md. For the cross-platform tool divergence, see ../cross-platform/askuserquestion-vs-ask-user-input-v0.md.