A new GitHub project With a very readable README:

JSON for Modern C++

by Niels Lohmann

From the README:

... You can create an object (deserialization) by appending _json to a string literal:

// create object from string literal
json j = "{ \"pi\": 3.141, \"happy\": true }"_json;

[Note: Or perhaps auto j = R"({ "pi": 3.141, "happy": true })"_json; --Ed.]

You can also get a string representation (serialize):

// explicit conversion to string
std::string s = j.to_string();