Hi @Lukas_Parsons,
Thanks for the detailed report. I’ve confirmed this is a server-side bug in the ACP agent, not a client-side rendering issue. The tool_call event is emitted before tool arguments are fully parsed, and a deduplication guard prevents it from being re-emitted once the full data is available. This affects all tool types, but MCP tools are worst-affected since their initial state is completely empty.
I reproduced this locally with a custom ACP client: even built-in tools show rawInput: {} despite completing successfully with actual parameters.
A related report exists at Cursor ACP raw input is missing. This is a known issue and our team is investigating.