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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 v2.1.121

updatedToolOutput Hook Property

What

PostToolUse hooks can now replace tool output for ALL tools (not just MCP tools) via the new updatedToolOutput field.

Details
  • Previously, only updatedMCPToolOutput was available, which only worked for MCP tools
  • The new updatedToolOutput field works for any tool (Bash, Read, Write, Edit, MCP, etc.)
  • The old updatedMCPToolOutput is retained but its description now says "Prefer updatedToolOutput, which works for all tools"
  • Validation error if hook output doesn't match expected tool output shape: "PostToolUse hook returned updatedToolOutput that does not match {tool}'s output shape"
Evidence

Hook output replacement (search for "updatedToolOutput", "Replaces the tool output before it is sent to the model")

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

See this entry in the whole of v2.1.121 →