JSON Cannot Access Unexported Struct Fields

Why This Happens

The encoding/json package uses reflection and can only access exported (capitalized) fields. Unexported fields are silently ignored during both marshaling and unmarshaling. This is a common source of confusion because there is no error, just empty or missing values.

The Problem

type User struct {
    name  string `json:"name"`  // unexported, ignored by json
    email string `json:"email"` // unexported, ignored by json
}

The Fix

type User struct {
    Name  string `json:"name"`
    Email string `json:"email"`
}

Step-by-Step Fix

1. 1

   Identify unexported fields

   Check if the struct fields that are missing from JSON output start with a lowercase letter.

2. 2

   Capitalize the fields

   Change the first letter of each field to uppercase to export it.

3. 3

   Add json tags

   Use struct tags like `json:"fieldName"` to control the JSON key names.