Capitals in struct fields

This is because only fields starting with a capital letter are exported, or in other words visible outside the curent package (and in the json package in this case).

Here is the part of the specifications refering to this: http://golang.org/ref/spec#Exported_identifiers

Still, you can unmarshall json fields that do no start with a capital letters using what is called "tags". With the json package, this is the syntax to use:

type Sample struct {
    Name string `json:"name"`
    Age  int    `json:"age"`
}

Refer to the documentation for more information about this.

json package only stringfiy fields start with capital letter. see http://golang.org/pkg/encoding/json/

Struct values encode as JSON objects. Each exported struct field becomes a member of the object, using the field name as the object key, unless the field is omitted for one of the reasons given below.

You need define the struct like this:

type Sample struct{
    Name string `json:"name"`
    Age int `json:"age"`
}