PHP json_decode() Function

What does json_decode() do?

json_decode() parses a JSON string. By default JSON objects become stdClass objects (access with ->); pass true as the second argument to get associative arrays instead (access with ['key']).

Syntax

json_decode(string $json, ?bool $associative = null, int $depth = 512, int $flags = 0): mixed

Parameters

• $json - The JSON string to decode. It must be UTF-8.
• $associative - true: objects become associative arrays. false/null: objects become stdClass (unless JSON_OBJECT_AS_ARRAY is set in flags).
• $depth - Maximum nesting depth.
• $flags - Bitmask such as JSON_THROW_ON_ERROR, JSON_BIGINT_AS_STRING, JSON_OBJECT_AS_ARRAY.

Return value

The decoded value (array, object, string, int, float, bool or null). Invalid JSON returns null, so check json_last_error() or use JSON_THROW_ON_ERROR.

json_decode() examples

Every example below shows the exact output it produces. Paste any of them into the editor above (or the online compiler) to run it.

1. Object vs associative array

<?php
$json = '{"name":"John","age":30,"city":"New York"}';

$obj = json_decode($json);
echo $obj->name . "\n";

$arr = json_decode($json, true);
echo $arr["city"] . "\n";

var_dump($arr);

Output:

John
New York
array(3) {
  ["name"]=>
  string(4) "John"
  ["age"]=>
  int(30)
  ["city"]=>
  string(8) "New York"
}

2. Read nested JSON

<?php
$json = '{"user":{"name":"Ann","roles":["admin","editor"]},"orders":[{"id":1,"total":9.5},{"id":2,"total":20}]}';
$data = json_decode($json, true);

echo $data["user"]["name"] . "\n";
echo $data["user"]["roles"][1] . "\n";
foreach ($data["orders"] as $order) {
    echo "Order {$order['id']}: {$order['total']}\n";
}

Output:

Ann
editor
Order 1: 9.5
Order 2: 20

3. Handle invalid JSON

<?php
$invalid = '{"name": "John",}';
var_dump(json_decode($invalid, true));
echo json_last_error_msg() . "\n";

try {
    json_decode($invalid, true, 512, JSON_THROW_ON_ERROR);
} catch (JsonException $e) {
    echo "Error: " . $e->getMessage() . "\n";
}

Output:

NULL
Syntax error
Error: Syntax error

4. Large integers

<?php
$json = '{"id": 12345678901234567890}';
var_dump(json_decode($json, true)["id"]);
var_dump(json_decode($json, true, 512, JSON_BIGINT_AS_STRING)["id"]);

Output:

float(1.2345678901234567E+19)
string(20) "12345678901234567890"

Decoding a JSON request body (save.php example)

APIs and JavaScript fetch() calls usually send JSON in the request body, not as form fields, so $_POST stays empty. Read the raw body from php://input, decode it with exceptions enabled, validate it, and store it with a prepared statement. This snippet needs a web server and database, so it is shown without output.

<?php
// save.php
header('Content-Type: application/json');

try {
    $data = json_decode(file_get_contents('php://input'), true, 512, JSON_THROW_ON_ERROR);
} catch (JsonException $e) {
    http_response_code(400);
    echo json_encode(['error' => 'Invalid JSON']);
    exit;
}

$name  = trim($data['name'] ?? '');
$email = filter_var($data['email'] ?? '', FILTER_VALIDATE_EMAIL);
if ($name === '' || $email === false) {
    http_response_code(422);
    echo json_encode(['error' => 'Name and a valid email are required']);
    exit;
}

$pdo = new PDO('mysql:host=localhost;dbname=app;charset=utf8mb4', 'user', 'password', [
    PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
]);
$stmt = $pdo->prepare('INSERT INTO contacts (name, email) VALUES (:name, :email)');
$stmt->execute(['name' => $name, 'email' => $email]);

echo json_encode(['id' => (int) $pdo->lastInsertId()]);

Common mistakes and gotchas

• null is ambiguous: json_decode("null") and invalid JSON both return null. Use JSON_THROW_ON_ERROR (PHP 7.3+) to tell them apart.
• Object vs array access: "Cannot use object of type stdClass as array" means you forgot the true argument (or should use ->).
• Trailing commas and single quotes are not valid JSON and cause a "Syntax error".
• Validation only: on PHP 8.3+, json_validate($json) checks syntax without building the array.