haphpiness

json_validate() — Validate Without Decoding

PHP 8.3 added phpjson_validate — a function that checks if a string is valid JSON without actually decoding it. Before this, you had to call json_decode() and check json_last_error(), which meant allocating memory for a data structure you didn't need.

// Before: decode the entire payload just to check if it's valid
$data = json_decode($input);
if (json_last_error() !== JSON_ERROR_NONE) {
    return 'Invalid JSON';
}

// After: validate without allocating a single array or object
if (!json_validate($input)) {
    return 'Invalid JSON';
}

// With depth limit — protect against deeply nested payloads
if (!json_validate($input, depth: 32)) {
    return 'JSON too deeply nested';
}

// Common pattern: validate first, decode only if valid
if (json_validate($payload)) {
    $data = json_decode($payload, true, flags: JSON_THROW_ON_ERROR);
    processData($data);
}

This is especially valuable for API gateways and middleware that need to validate JSON bodies before routing them — you skip the memory cost of decoding entirely.