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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 v2.1.242

New tool_host_result system message in stream-json output

Use it now
Useful3 Signal3
Agents

Tool host output arrives as its own system message in stream-json, easier to script against.

--output-format stream-json
What

Output from a tool host (a separate process that runs a tool on Claude Code's behalf) now arrives as its own system message in --output-format stream-json, so scripts can read it directly instead of parsing it out of an attachment.

Details
  • The message carries the tool_use_id, the host name and its working directory, an optional disposition and label, an unverified flag, and the output lines.
  • No flag gates it; it is emitted whenever the underlying attachment appears.
Evidence

tool_host_result

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

Related

Other releases about the same thing. Found by shared names or similar wording; neither means one caused the other.

See this entry in the whole of v2.1.242 →