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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 v2.1.31 4 Feb 2026

Tool Names in Messages [In Development]

What

A feature that changes how deferred tool search prompts are constructed when tool names are injected into messages.

Status

Feature-flagged via tengu_tst_names_in_messages (default false)

Details

Controlled by CLAUDE_CODE_TST_NAMES_IN_MESSAGES environment variable or the tengu_tst_names_in_messages feature flag
When enabled, returns a different tool search prompt variant (CS9) instead of the default
Appears to change how the ToolSearchTool presents its available tools list

Evidence

Tool names in messages feature (search for "CLAUDE_CODE_TST_NAMES_IN_MESSAGES", gated by tengu_tst_names_in_messages)

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

See this entry in the whole of v2.1.31 →