Cookie Basics

Cookies are small pieces of data stored in the browser and sent back to the server with every request to the same domain. PHP reads incoming cookies via $_COOKIE and writes them with setcookie().

Cookies set with setcookie() are available in $_COOKIE only on the next request.
Always pass the full options array (PHP 7.3+) rather than positional arguments.
To delete a cookie, set its expiry to a time in the past.

Example

<?php
// Set a cookie (must be called before any output)
setcookie('theme', 'dark', [
    'expires'  => time() + (86400 * 30), // 30 days
    'path'     => '/',
    'domain'   => 'example.com',
    'secure'   => true,  // HTTPS only
    'httponly' => true,  // not accessible via JS
    'samesite' => 'Lax',
]);

// Read a cookie on subsequent requests
$theme = $_COOKIE['theme'] ?? 'light';
echo "Current theme: $theme";

// Update a cookie — just call setcookie() again with the same name
setcookie('theme', 'light', [
    'expires'  => time() + (86400 * 30),
    'path'     => '/',
    'httponly' => true,
    'samesite' => 'Lax',
]);

// Delete a cookie — set expiry in the past
setcookie('theme', '', [
    'expires'  => time() - 3600,
    'path'     => '/',
]);

// Check if a cookie exists
if (isset($_COOKIE['theme'])) {
    echo "Theme preference found: " . htmlspecialchars($_COOKIE['theme']);
}

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Pro Tip

Tip: Prefer the array-based setcookie() syntax (PHP 7.3+). It is far less error-prone than the old positional argument form, especially for the samesite attribute which cannot be set positionally in older PHP versions.

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