How can I pretty-print JSON using Go?

By pretty-print, I assume you mean indented, like so

{
    "data": 1234
}

rather than

{"data":1234}

The easiest way to do this is with MarshalIndent, which will let you specify how you would like it indented via the indent argument. Thus, json.MarshalIndent(data, "", " ") will pretty-print using four spaces for indentation.