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DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

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Claude Code v2.1.9

ENABLE_TOOL_SEARCH Percentage Control

What

The ENABLE_TOOL_SEARCH environment variable now supports percentage-based control with the auto:N syntax.

Usage
ENABLE_TOOL_SEARCH=auto:50  # 50% tool search probability
ENABLE_TOOL_SEARCH=auto:0   # Equivalent to "tst" (always tool search)
ENABLE_TOOL_SEARCH=auto:100 # Equivalent to standard/mcp-cli modes
Details
  • Values are clamped between 0-100
  • Invalid values log a warning and fall back to defaults
  • Provides fine-grained control over tool search behavior
Evidence

DX0() at line 292496 (auto percentage parser, contains "Invalid ENABLE_TOOL_SEARCH value", "expected auto:N where N is a number")

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

See this entry in the whole of v2.1.9 →