Working with JSON in Go: Encode, Decode, and Tag Structs

JSON (JavaScript Object Notation) is a widely used data format in APIs and web applications. Go provides strong support for JSON through the standard encoding/json package. In this article, you’ll learn how to parse JSON into structs, generate JSON from Go data, use struct tags, and work with nested or dynamic structures.

In this article, you’ll learn:

How to encode Go structs to JSON
How to decode JSON into Go structs
Using JSON tags to customize field names
Working with maps and dynamic JSON
Handling nested JSON structures
Best practices and error handling

Encoding Structs to JSON

Use json.Marshal to convert Go structs into JSON strings:

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

func main() {
    user := User{"Alice", "alice@example.com", 30}

    jsonData, err := json.Marshal(user)
    if err != nil {
        log.Fatal(err)
    }

    fmt.Println(string(jsonData))
}

Decoding JSON into Structs

Use json.Unmarshal to parse JSON into a struct:

var jsonInput = []byte(`{"name":"Bob","email":"bob@example.com","age":25}`)

var user User
err := json.Unmarshal(jsonInput, &user)
if err != nil {
    log.Fatal(err)
}

fmt.Println(user.Name, user.Email, user.Age)

Using Struct Tags

By default, Go uses struct field names as JSON keys. Use tags to customize:

type Product struct {
    ID    int     `json:"id"`
    Name  string  `json:"name"`
    Price float64 `json:"price"`
}

Working with Maps and Dynamic JSON

Use map[string]interface{} when the structure is not fixed:

var data = []byte(`{"status":"ok","code":200}`)

var result map[string]interface{}
err := json.Unmarshal(data, &result)
if err != nil {
    log.Fatal(err)
}

fmt.Println(result["status"], result["code"])

Nested JSON Example

type Address struct {
    City    string `json:"city"`
    Country string `json:"country"`
}

type Employee struct {
    Name    string  `json:"name"`
    Address Address `json:"address"`
}

JSON:

 {
  "name": "John",
  "address": {
    "city": "Jakarta",
    "country": "Indonesia"
  }
}

Encode JSON to File

f, err := os.Create("data.json")
if err != nil {
    log.Fatal(err)
}
defer f.Close()

json.NewEncoder(f).Encode(user)

Decode JSON from File

f, err := os.Open("data.json")
if err != nil {
    log.Fatal(err)
}
defer f.Close()

json.NewDecoder(f).Decode(&user)

Best Practices

Always handle encoding/decoding errors
Use struct tags for clean JSON output
Validate incoming JSON before using
Use omitempty tag to skip empty fields

Conclusion

Working with JSON in Go is simple, powerful, and type-safe. Whether you’re building APIs, reading config files, or exchanging data between systems, the encoding/json package gives you everything you need.

Next, we’ll dive into building a REST API in Go using net/http.

Happy coding!

BUANACODING