// Created on savesnippets.com · https://savesnippets.com/OT1aZG5HySsKcT
<?php
function logJson(string $path, string $level, string $message, array $context = []): void {
    $entry = json_encode([
        'ts'      => date('c'),
        'level'   => strtoupper($level),
        'msg'     => $message,
        'context' => $context,
        'pid'     => getmypid(),
    ], JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE);
    file_put_contents($path, $entry . PHP_EOL, FILE_APPEND | LOCK_EX);
}

logJson('/var/log/myapp.log', 'info',  'user signed in', ['user_id' => 42, 'ip' => '10.0.0.1']);
logJson('/var/log/myapp.log', 'error', 'payment failed', ['order_id' => 9001, 'reason' => 'card_declined']);