Unclear Whether these hook types behave differently from before, or are only described more fully, is not clear.
What
Hooks are commands or prompts you configure to run automatically at certain moments, such as before a tool runs. Two new hook types are being added:
- An
agenthook type, with the fieldsprompt,if,timeout,model,status_messageandonce. - An
mcp_toolhook type, which calls a tool on an MCP server (an add-on that supplies tools), withserver,tool,input,if,timeout,status_messageandonce. - Hooks of these types are only accepted when a list fetched from Anthropic's remote settings,
tengu_woven_ladder, contains "agent" or "mcp_tool". The list defaults to empty, and with it empty these hooks are treated as an unknown kind, as before. Nothing has been read about this list yet. mcp_toolhooks are kept in a separate "not connected" group, their number is capped, and their server name must match a pattern. A pattern for plugin-qualified names (plugin:<name>:...) is also added.- A new error says
mcp_toolhooks are not available for a hook event that has no MCP connection behind it, naming the event.
Before, only prompt and command hooks were read.
Why
Once enabled, hooks could start a subagent or call an MCP tool directly. If you configure an mcp_tool hook on an event that does not support it, you now get an explicit error.
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Whether these hook types behave differently from before, or are only described more fully, is not clear.