You'll noticeTier: how much it should matter to you
2Useful: my rating, 1 to 5
2Signal: worth watching, 1 to 5
HooksArea: what it touches
ImprovementsKind: in v2.1.323,
ImprovementsSection of the release
What
MCP servers supply extra tools to Claude Code. A hook is a script or rule that runs at a set point. Hooks that run when the tool list is built, called tool.list hooks, can remove tools from that list.
Before an MCP tool call goes ahead, Claude Code now checks those hooks. If one removed the tool, the call is refused with "mcp_call refused: a tool.list hook removed the tool". Before, only a check for the cloud browser ran at that point.
Why
Removing a tool with a hook now also blocks calls to it, not only its appearance in the list.
