Misleading _noargs parameter in TaskList tool schema causes repeated agent errors

GitHub Issue for Anthropic Claude Code

Title

Misleading _noargs parameter in TaskList tool schema causes repeated agent errors

Description

Problem

The TaskList tool's JSON Schema includes a _noargs parameter that misleads agents into attempting to pass parameters, resulting in validation errors and failure loops.

Evidence

In session 4bd4f262-0f63-409e-b853-7d051cb84b94, the agent made 11 consecutive failed calls to TaskList with invalid parameters before user intervention.

Current Schema (Problematic)

{
  "name": "TaskList",
  "parameters": {
    "properties": {
      "_noargs": {
        "description": "unused placeholder (tool takes no arguments)",
        "type": "string"
      }
    },
    "type": "object"
  }
}

Why This is Misleading

1. The presence of _noargs suggests parameters can be passed
2. Agents attempt to use _noargs based on the schema
3. Both TaskList(file_path=...) and TaskList(_noargs="unused") fail
4. Error messages don't provide correct usage examples

Actual Behavior

<!-- ❌ Agent sees _noargs and tries this -->
<invoke name="TaskList">
<parameter name="_noargs">unused</parameter>
</invoke>
<!-- Error: unexpected parameter -->

<!-- ✅ Correct usage not obvious from schema -->
<invoke name="TaskList"></invoke>

Impact

• Agents enter failure loops (11+ retries observed)
• User must manually interrupt and correct
• Other tools using _noargs pattern likely affected

Proposed Solutions

Option A: Remove parameters entirely (Recommended)

{
  "name": "TaskList",
  "description": "Use this tool to list all tasks. This tool takes NO parameters."
}

Option B: Explicit prohibition

{
  "name": "TaskList",
  "parameters": {
    "type": "object",
    "properties": {},
    "additionalProperties": false,
    "description": "This tool accepts NO parameters"
  }
}

Option C: Better error messages

Error: TaskList does not accept any parameters

Correct usage:
<invoke name="TaskList"></invoke>

Common mistake: Confusing TaskList (list tasks) with Read (read files)

Workaround Created

I've created an auto-fixer MCP server inspired by LangChain's tool_retry pattern:

• Detects parameter errors automatically
• Applies fix rules (e.g., TaskList → empty params)
• Auto-retries with corrected parameters
• Reduces 11 failures → 1 success

Code: https://github.com/[your-repo]/tool-call-auto-fixer

Related Issues

Search results show other users experiencing "Invalid tool parameters" errors (#15390, #23874)

Recommendation

Audit all tools using _noargs pattern and either:

1. Remove the parameter definition entirely
2. Add additionalProperties: false
3. Improve validation error messages with usage examples

---

Environment:

• Claude Code Version: Latest
• Model: Claude Opus 4.7
• Platform: Windows 11

Session ID: 4bd4f262-0f63-409e-b853-7d051cb84b94