You'll notice
Tool-call error messages now include specific custom validation messages from Zod
What
When a tool call fails validation, Claude Code builds an error message describing what went wrong, such as missing, unexpected, or wrong-type parameters. That message now also includes any custom validation error messages produced by the validation library (Zod) when a check is specifically marked as "custom".
Why
This surfaces more specific, tool-author-written explanations of why a call failed, instead of only generic parameter-shape errors.