[BUG] Incorrect token counts per MCP tool

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?

/context reports incorrect token count for MCP tool. The number comes from the from

https://api.anthropic.com/v1/messages/count_tokens?beta=true

API call.

CC reports cca 600 tokens per MCP tool. I have extracted tool definition from the system prompt and it amounts around 130 tokens (600 chars).

If I disable the MCP (has multiple tools), the total amount of tokens used reported by /context command matches my calculation and not sum of all MCP tools reported by CC.

What Should Happen?

Fix token count for MCP tools.

Error Messages/Logs

Steps to Reproduce

Trivial check: Run /context with MCP tools. Check total token count. Disable MCPs and run /context again. Sum of all tool tokens reported does not match of context size reductions.

Claude Model

Sonnet (default)

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.0.75

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_