Unclear It is not clear which server settings cause an mcp_tool hook to be refused.
An mcp_tool hook is a hook (an action set to run automatically at certain points) that calls a tool on an MCP server. Claude Code used to refuse such a hook only for the account memory server. It now also checks any server's configuration for a refusal, both before and after connecting to it. A refused call is reported as withheld.
Hook matchers, the patterns that decide which tools a hook applies to, now treat MCP tools that belong to Claude Code itself the same way as built-in tools, including matching them by their group name. If the same hook would be triggered twice through that group routing, it now runs only once.
This changes which hooks fire for MCP tools, so a hook that targets one of these tools may now run, run once instead of twice, or be refused.
It is not clear which server settings cause an `mcp_tool` hook to be refused.