JSON Formatter, Minifier, and Validator in Go — Code Examples

JSON parsing and serialisation is built into every major language. Here is how to parse a JSON string, format (pretty-print) JSON, and handle common edge cases in each language.

Go's encoding/json package uses struct tags for mapping. json.Marshal() serializes and json.Unmarshal() parses.

package main

import (
    "encoding/json"
    "fmt"
)

type User struct {
    Name string `json:"name"`
    Age  int    `json:"age"`
    Email string `json:"email,omitempty"` // omit if empty
}

func main() {
    // Parse JSON → struct
    data := []byte(`{"name":"Alice","age":30}`)
    var user User
    if err := json.Unmarshal(data, &user); err != nil {
        panic(err)
    }
    fmt.Println(user.Name) // Alice

    // Serialize struct → JSON
    out, err := json.Marshal(user)
    if err != nil {
        panic(err)
    }
    fmt.Println(string(out)) // {"name":"Alice","age":30}

    // Pretty-print
    pretty, _ := json.MarshalIndent(user, "", "  ")
    fmt.Println(string(pretty))

    // Parse into map (for unknown structure)
    var m map[string]any
    json.Unmarshal(data, &m)
    fmt.Println(m["name"]) // Alice
}

• json.Unmarshal() requires a pointer — pass &variable, not variable.
• Use omitempty in struct tags to skip zero-value fields in output.
• json.Decoder is more efficient than json.Unmarshal when reading from an io.Reader (HTTP body, file).

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