Function has_invalid_annotation 

pub fn has_invalid_annotation(schema: &Value) -> bool

Whether schema carries any x-mcp-header annotation the transport specification forbids.

For a client: “Clients using the Streamable HTTP transport MUST reject tool definitions where any x-mcp-header value violates these constraints”, which means leaving the tool out of tools/list. An annotation is invalid when its name is not a header token, when it sits on a type other than string, integer or boolean, when it is reached through anything but properties, or when two annotations name the same header.