[BUG] Tool search has broken ranking, causing Claude to fail to find a tool despite exact name match

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?

Observation:

• Claude appears to know that a tool is a deferred tool but repeatedly fails to find it. Claude fails to load & apply tools that its search does not return.
• The ranking algorithm for Claude's tool search often ranks tools higher that are not a good match, e.g. search for find symbol with Serena MCP's tool set can fail to surface the tool actually named find_symbol. Claude never searches for more than 5 matches on its own and therefore does not find & apply the tool without assistance.

This affects Claude Code and Claude Desktop alike.
Look at this:

<img width="737" height="704" alt="Image" src="https://github.com/user-attachments/assets/fb788296-e803-47d0-aa03-df021d2e303e" />

<img width="751" height="763" alt="Image" src="https://github.com/user-attachments/assets/5d7f485c-92d1-4cff-9aaa-5d93f400351e" />

<img width="731" height="652" alt="Image" src="https://github.com/user-attachments/assets/fb8aa395-906e-4a16-8ba7-45532733622b" />

What Should Happen?

The ranking algorithm should be improved to surface exact name matches immediately. Name match should have more weight than description match (which currently appears to prefer longer descriptions over shorter ones and is not focused on an actual semantic match, unfortunately).

Error Messages/Logs

Steps to Reproduce

1. Use Claude with an MCP server like Serena, which has a large number of related tools.
2. Make Claude apply tool search and observe its failures to find the relevant tools (even though it knows they exist)

Claude Model

Opus

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.1.169

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

_No response_