[DOCS] Clarify default behavior of MCP Tool Search in `docs/en/mcp.md`

Documentation Type

Unclear/confusing documentation

Documentation Location

https://code.claude.com/docs/en/mcp#configure-tool-search

Section/Topic

The "Scale with MCP Tool Search" section, specifically under the "Configure tool search" heading.

Current Documentation

Currently, the documentation states:

"Control tool search behavior with the ENABLE_TOOL_SEARCH environment variable:"

It then lists a table where auto is marked as (default).

What's Wrong or Missing?

The phrasing "Control tool search behavior with..." implies that this is an opt-in feature or that the user must set an environment variable to activate it.

According to the Changelog for v2.1.7, this feature was "Enabled MCP tool search auto mode by default for all users." While the table in the documentation does technically say "(default)" next to auto, the introductory text suggests that configuration is a requirement rather than an override option. Users might waste time setting up environment variables for behavior they already have out-of-the-box.

Suggested Improvement

The text should explicitly state that the feature is active by default and that configuration is only necessary if the user wishes to disable it or modify the threshold.

Suggested text:

"Tool search is enabled by default in auto mode (activating when MCP tools exceed 10% of context). No configuration is required to use this feature. To customize the threshold or disable tool search entirely, you can set the ENABLE_TOOL_SEARCH environment variable:"

Impact

High - Prevents users from using a feature

Additional Context

• Changelog v2.1.7: Explicitly states "Enabled MCP tool search auto mode by default for all users."
• Settings Documentation: docs/en/settings.md correctly identifies auto as the default, but the primary MCP guide should be clearer about the "zero-config" nature of this feature.