Mostly, no. Whether its the client sending (statically) bad data or the server returning (statically) bad data, schema validation on the other end (assuming somehow it is allowed by the toolchain on the sending end) should reject it before it gets to the custom code of the MCP server or MCP client.
For arguments that are the right type but wrong because of the state of the universe, yes, the server receiving it should send a useful error message back to the client. But that's a different issue.
Mostly, no. Whether its the client sending (statically) bad data or the server returning (statically) bad data, schema validation on the other end (assuming somehow it is allowed by the toolchain on the sending end) should reject it before it gets to the custom code of the MCP server or MCP client.
For arguments that are the right type but wrong because of the state of the universe, yes, the server receiving it should send a useful error message back to the client. But that's a different issue.