Online JSON Parser & Formatter — Format, validate, and explore JSON with syntax highlighting and tree view

import json
from pathlib import Path

# Parse a JSON string
raw = '{"name": "Alice", "age": 30, "active": true}'
user = json.loads(raw)
print(user["name"])  # Alice

# Serialize to a formatted JSON string
data = {
    "id": 1,
    "tags": ["dev", "api"],
    "address": {"city": "NYC", "zip": "10001"},
    "score": None,  # becomes null in JSON
}
pretty = json.dumps(data, indent=2, ensure_ascii=False)

# Read JSON from a file
config = json.loads(Path("config.json").read_text())

# Write JSON to a file
Path("output.json").write_text(
    json.dumps(data, indent=2)
)

# Custom encoder for non-serializable types
from datetime import datetime

class DateEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, datetime):
            return obj.isoformat()
        return super().default(obj)

json.dumps({"now": datetime.now()}, cls=DateEncoder)

// Define a typed interface for JSON data
interface User {
  name: string;
  age: number;
  active: boolean;
  tags: string[];
  address: { city: string; zip: string };
}

// Type-safe parsing with validation
function parseUser(raw: string): User {
  const data: unknown = JSON.parse(raw);
  if (
    typeof data === "object" && data !== null &&
    "name" in data && "age" in data
  ) {
    return data as User;
  }
  throw new Error("Invalid user JSON");
}

// Generic fetch helper with typed response
async function fetchJson<T>(url: string): Promise<T> {
  const res = await fetch(url);
  if (!res.ok) throw new Error(`HTTP ${res.status}`);
  return res.json() as Promise<T>;
}

const user = await fetchJson<User>("/api/user/1");

// Partial updates with Pick / Omit
type UserUpdate = Partial<Pick<User, "name" | "age">>;
const patch: UserUpdate = { name: "Bob" };
await fetch("/api/user/1", {
  method: "PATCH",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify(patch),
});

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.reflect.TypeToken;
import java.util.List;
import java.util.Map;

public class JsonExample {
    // Define a POJO for JSON mapping
    record User(String name, int age, boolean active, List<String> tags) {}

    public static void main(String[] args) {
        Gson gson = new GsonBuilder().setPrettyPrinting().create();

        // Deserialize JSON string to object
        String raw = """
            {"name":"Alice","age":30,"active":true,"tags":["dev","api"]}
            """;
        User user = gson.fromJson(raw, User.class);
        System.out.println(user.name()); // Alice

        // Serialize object to JSON
        String json = gson.toJson(user);

        // Parse into a generic Map
        Map<String, Object> map = gson.fromJson(raw,
            new TypeToken<Map<String, Object>>(){}.getType());

        // Parse a JSON array
        String arr = """
            [{"name":"Alice"},{"name":"Bob"}]
            """;
        List<User> users = gson.fromJson(arr,
            new TypeToken<List<User>>(){}.getType());
    }
}

package main

import (
	"encoding/json"
	"fmt"
	"os"
)

// Struct tags control JSON field names
type User struct {
	Name    string   `json:"name"`
	Age     int      `json:"age"`
	Active  bool     `json:"active"`
	Tags    []string `json:"tags,omitempty"`
	Address *Address `json:"address,omitempty"`
}

type Address struct {
	City string `json:"city"`
	Zip  string `json:"zip"`
}

func main() {
	// Unmarshal JSON into a struct
	raw := `{"name":"Alice","age":30,"active":true}`
	var user User
	json.Unmarshal([]byte(raw), &user)
	fmt.Println(user.Name) // Alice

	// Marshal struct to indented JSON
	out, _ := json.MarshalIndent(user, "", "  ")
	fmt.Println(string(out))

	// Decode from a stream (file, HTTP body, etc.)
	file, _ := os.Open("data.json")
	defer file.Close()
	var data User
	json.NewDecoder(file).Decode(&data)

	// Dynamic parsing with map
	var generic map[string]interface{}
	json.Unmarshal([]byte(raw), &generic)
}

use serde::{Deserialize, Serialize};
use serde_json::{json, Value};

// Derive macros for automatic JSON serialization
#[derive(Debug, Serialize, Deserialize)]
struct User {
    name: String,
    age: u32,
    active: bool,
    #[serde(default)]
    tags: Vec<String>,
    #[serde(skip_serializing_if = "Option::is_none")]
    address: Option<Address>,
}

#[derive(Debug, Serialize, Deserialize)]
struct Address {
    city: String,
    zip: String,
}

fn main() -> serde_json::Result<()> {
    // Deserialize from a JSON string
    let raw = r#"{"name":"Alice","age":30,"active":true}"#;
    let user: User = serde_json::from_str(raw)?;
    println!("{}", user.name); // Alice

    // Serialize to a pretty JSON string
    let json = serde_json::to_string_pretty(&user)?;

    // Build JSON dynamically with the json! macro
    let val = json!({
        "status": "ok",
        "count": 42,
        "items": ["a", "b", "c"]
    });

    // Parse into an untyped Value for dynamic access
    let v: Value = serde_json::from_str(raw)?;
    println!("{}", v["name"]); // "Alice"

    Ok(())
}

<?php
// Decode a JSON string into an associative array
$raw = '{"name":"Alice","age":30,"active":true}';
$user = json_decode($raw, associative: true);
echo $user['name']; // Alice

// Decode into an object (stdClass)
$obj = json_decode($raw);
echo $obj->name; // Alice

// Encode an array to a formatted JSON string
$data = [
    'id' => 1,
    'tags' => ['dev', 'api'],
    'address' => ['city' => 'NYC', 'zip' => '10001'],
    'score' => null,
];
$json = json_encode($data, JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE);

// Error handling for malformed JSON
$bad = json_decode('invalid json');
if (json_last_error() !== JSON_ERROR_NONE) {
    echo 'Parse error: ' . json_last_error_msg();
}

// Read and write JSON files
$config = json_decode(file_get_contents('config.json'), true);
file_put_contents('output.json', json_encode($data, JSON_PRETTY_PRINT));

require 'json'

# Parse a JSON string into a Hash
raw = '{"name":"Alice","age":30,"active":true}'
user = JSON.parse(raw)
puts user['name'] # Alice

# Parse with symbolized keys
user = JSON.parse(raw, symbolize_names: true)
puts user[:name] # Alice

# Generate formatted JSON from a Hash
data = {
  id: 1,
  tags: %w[dev api],
  address: { city: 'NYC', zip: '10001' },
  score: nil  # becomes null in JSON
}
puts JSON.pretty_generate(data)

# Read JSON from a file
config = JSON.parse(File.read('config.json'))

# Write JSON to a file
File.write('output.json', JSON.pretty_generate(data))

# Custom serialization with #to_json
class User
  attr_accessor :name, :age
  def to_json(*args)
    { name: @name, age: @age }.to_json(*args)
  end
end

using System.Text.Json;
using System.Text.Json.Serialization;

// Define a record for JSON mapping
public record User(
    string Name,
    int Age,
    bool Active,
    string[] Tags
);

// Deserialize JSON into a typed object
var raw = """{"name":"Alice","age":30,"active":true,"tags":["dev"]}""";
var opts = new JsonSerializerOptions {
    PropertyNameCaseInsensitive = true
};
var user = JsonSerializer.Deserialize<User>(raw, opts)!;
Console.WriteLine(user.Name); // Alice

// Serialize to indented JSON
var json = JsonSerializer.Serialize(user, new JsonSerializerOptions {
    WriteIndented = true,
    PropertyNamingPolicy = JsonNamingPolicy.CamelCase
});

// Parse dynamic JSON with JsonDocument
using var doc = JsonDocument.Parse(raw);
var root = doc.RootElement;
var name = root.GetProperty("name").GetString();

// Work with JsonNode for mutable access
var node = JsonNode.Parse(raw)!;
node["age"] = 31;
Console.WriteLine(node.ToJsonString());

import Foundation

// Define a Codable struct for JSON mapping
struct User: Codable {
    let name: String
    let age: Int
    let active: Bool
    let tags: [String]?
}

// Decode JSON data into a struct
let raw = #"{"name":"Alice","age":30,"active":true}"#
let data = raw.data(using: .utf8)!
let decoder = JSONDecoder()
let user = try decoder.decode(User.self, from: data)
print(user.name) // Alice

// Encode struct to formatted JSON
let encoder = JSONEncoder()
encoder.outputFormatting = [.prettyPrinted, .sortedKeys]
let json = try encoder.encode(user)
print(String(data: json, encoding: .utf8)!)

// Custom key mapping with CodingKeys
struct ApiResponse: Codable {
    let userId: Int
    let createdAt: String

    enum CodingKeys: String, CodingKey {
        case userId = "user_id"
        case createdAt = "created_at"
    }
}

// Dynamic parsing with JSONSerialization
let obj = try JSONSerialization.jsonObject(with: data) as! [String: Any]
let name = obj["name"] as? String

import kotlinx.serialization.*
import kotlinx.serialization.json.*

// Data class with serialization annotations
@Serializable
data class User(
    val name: String,
    val age: Int,
    val active: Boolean,
    val tags: List<String> = emptyList()
)

fun main() {
    val json = Json { prettyPrint = true; ignoreUnknownKeys = true }

    // Deserialize JSON string to object
    val raw = """{"name":"Alice","age":30,"active":true}"""
    val user = json.decodeFromString<User>(raw)
    println(user.name) // Alice

    // Serialize object to JSON
    val output = json.encodeToString(user)

    // Dynamic parsing with JsonElement
    val element = json.parseToJsonElement(raw)
    val name = element.jsonObject["name"]?.jsonPrimitive?.content

    // Build JSON dynamically
    val built = buildJsonObject {
        put("status", "ok")
        put("count", 42)
        putJsonArray("items") {
            add("a"); add("b"); add("c")
        }
    }
    println(json.encodeToString(built))
}