[BUG] MCP tool names with UUIDs exceed 64-character API limit

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

When connecting to certain MCP servers (e.g., Notion), Claude Code generates tool names that exceed the 64-character limit, causing API errors and getting stuck in a loop.

What Should Happen?

Tool names should be kept within the 64-character API limit. The UUID prefix should be shortened or an alternative naming scheme used.

Error Messages/Logs

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.40.content.0.tool_result.content.0.tool_reference.tool_name: String should have at most 64 characters"}}

Problematic tool name: mcp__5ae21acc-5fda-4317-803f-1a7a34a38c3d__notion-update-data-source (71 characters)

Steps to Reproduce

1. Install the Notion MCP connector via Claude Desktop or Claude Code
2. Start a session that uses the Notion MCP tools
3. The tool name generated includes a UUID prefix, making it exceed 64 characters
4. API errors occur and the session gets stuck in a loop

<img width="2048" height="1152" alt="Image" src="https://github.com/user-attachments/assets/ae1dec9e-cb58-43d6-8ae1-3292a106c4c4" />

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

2.1.12 (Claude Code)

Claude Code Version

2.1.12 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

The issue persists in the session even after removing the MCP server from configuration. Starting a new session resolves it since the problematic tool name is no longer in the conversation history.