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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 v2.1.118 22 Apr 2026

MCP Tool Hooks (mcp_tool)

What

A new hook type that invokes an MCP server tool as the hook action, as an alternative to bash/command hooks.

Details

Configure with type: "mcp_tool" in hook definitions
Specify server (name of an already-configured MCP server) and tool (tool name on that server)
Supports arguments object with ${path} interpolation from hook input JSON
Optional timeout field for per-call timeout in seconds
Reads X-Mcp-Error-Code header from 401 responses for better error diagnostics
Not available for all hook events — logs "mcp_tool hooks are not available for the '<event>' hook event" when unsupported

Evidence

Hook type definition (search for "mcp_tool") and MCP tool schema fields (search for "Name of an already-configured MCP server to invoke").

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

See this entry in the whole of v2.1.118 →