PHP JSON

JSON (JavaScript Object Notation) is a lightweight, text-based data-interchange format. It is the most common way to send and receive data between a PHP backend and a browser, a mobile app, or another web service (most REST APIs speak JSON). This guide covers everything you need to work with JSON in PHP: turning PHP data into JSON with json_encode, turning JSON back into PHP data with json_decode, formatting the output, and handling errors safely.

PHP ships JSON support in its core (the ext-json extension is bundled and enabled by default since PHP 8.0), so there is nothing to install.

What JSON looks like

JSON represents data as key-value pairs inside objects ({ }) and ordered lists inside arrays ([ ]). Values can be strings, numbers, booleans, null, arrays, or nested objects:

{
  "name": "John",
  "age": 30,
  "active": true,
  "roles": ["admin", "editor"]
}

The two functions you will use almost every time are:

• json_encode($value) — PHP value → JSON string (serialize).
• json_decode($json) — JSON string → PHP value (deserialize).

Encoding: PHP to JSON with json_encode

json_encode() converts a PHP value — typically an array or object — into a JSON string.

Encoding an associative array

An associative array becomes a JSON object, while an indexed array (sequential integer keys starting at 0) becomes a JSON array:

<?php

echo json_encode(["red", "green", "blue"]);
// ["red","green","blue"]

?>

Formatting the output

By default json_encode produces compact JSON on a single line, which is ideal for sending over the network. When you want human-readable output (for logging or debugging), pass the JSON_PRETTY_PRINT flag. Flags are combined with the bitwise | operator:

<?php

$data = [
    "user" => ["name" => "Jane", "roles" => ["admin", "editor"]],
    "active" => true,
];

echo json_encode($data, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES);

?>

This prints nicely indented JSON:

{
    "user": {
        "name": "Jane",
        "roles": [
            "admin",
            "editor"
        ]
    },
    "active": true
}

Other useful flags: JSON_UNESCAPED_SLASHES (keeps / instead of \/) and JSON_UNESCAPED_UNICODE (keeps characters like é instead of é).

Decoding: JSON to PHP with json_decode

json_decode() converts a JSON string back into a PHP value. By default it returns objects, but passing true as the second argument returns associative arrays instead — which are usually easier to loop over:

Without the true argument, you get a stdClass object and access values with the -> arrow notation instead of [ ]:

Use true when you want an array; omit it when you prefer object syntax. Both contain the same data.

Encoding a custom object

json_encode also works on objects. When you need to build a JSON structure on the fly, the empty stdClass object lets you attach properties dynamically. (For full classes, see PHP Classes and Objects.)

Public properties of any object are included automatically; private and protected properties are skipped unless the class implements the JsonSerializable interface.

Handling errors

JSON parsing can fail — a malformed string, an unterminated quote, or a trailing comma will all break decoding. When json_decode fails it returns null, so you must distinguish a real null value from an error. Check json_last_error() (or read json_last_error_msg() for a human-readable message):

<?php

$badJson = '{invalid}';
$result = json_decode($badJson);

if (json_last_error() !== JSON_ERROR_NONE) {
    echo "JSON error: " . json_last_error_msg();
    // JSON error: Syntax error
}

?>

Since PHP 7.3 you can instead pass the JSON_THROW_ON_ERROR flag to make both functions throw a JsonException, which fits cleanly into try/catch blocks:

<?php

try {
    $data = json_decode('{invalid}', true, 512, JSON_THROW_ON_ERROR);
} catch (JsonException $e) {
    echo "Could not parse JSON: " . $e->getMessage();
}

?>

Note: json_decode has a depth limit (512 levels by default, the third argument). Very deeply nested JSON will fail with a JSON_ERROR_DEPTH error unless you raise it.

Common use case: reading a JSON request body

When a client sends JSON to a PHP endpoint (as most APIs do), the body arrives as raw input rather than $_POST. Read it with php://input and decode it:

<?php

$body = file_get_contents("php://input");
$data = json_decode($body, true);

// echo a JSON response back to the client
header("Content-Type: application/json");
echo json_encode(["received" => $data]);

?>

Conclusion

JSON is the standard format for exchanging data in modern web applications, and PHP makes it straightforward to work with:

• Use json_encode to turn arrays and objects into JSON; add JSON_PRETTY_PRINT for readable output.
• Use json_decode to turn JSON back into PHP — pass true for an array, omit it for an object.
• Always check for errors with json_last_error() or JSON_THROW_ON_ERROR before trusting decoded data.

With these tools you can confidently send and receive JSON between your PHP code, databases, browsers, and external web services.

Practice