Is it always necessary to install the

ContentNegotiation

feature in the server to receive & send serialized (JSON encoded) objects? If the expected, exact content type is specified on both server and receiver, I don't see why

ContentNegotiation

needs to be a hard requirement - I thought this was only about dynamically negotiating a variable content & type at run-time?

It's not necessary. You can do this for example without installing the feature:

get("/") {
                call.respond(TextContent("{\"key\": \"value\"}", contentType = ContentType.Application.Json))
            }

And you can test request content type:

if (call.request.contentType() == ContentType.Application.Json) {
                    val text = call.receiveText()
                    // deserialize text
                }