What is the PHP __debugInfo Magic Method?

The __debugInfo() magic method in PHP is a specialized tool that allows developers to customize how an object behaves when it is output by debugging functions like var_dump(). By default, dumping an object prints all of its public, protected, and private properties. By implementing __debugInfo(), you can control exactly which properties are displayed, obfuscate sensitive data, or simplify the output of complex objects to make debugging much cleaner and safer.

Why Use __debugInfo()?

When debugging PHP applications, standard object dumps can sometimes be overwhelming or insecure. The __debugInfo() method solves two major problems:

  1. Protecting Sensitive Data: Objects often hold sensitive information such as database passwords, API keys, or personally identifiable information (PII). Using __debugInfo() prevents this data from being printed to screen outputs or error logs during debugging.
  2. Reducing Output Noise: Complex objects—especially those utilizing dependency injection or containing circular references—can produce thousands of lines of output when dumped. __debugInfo() allows you to filter out unnecessary dependency objects and show only the relevant state of the class.

How it Works

The __debugInfo() method must be declared inside your class as a public method, and it must return an array. This array represents the properties and values that will be shown in the debug output.

Here is a practical example demonstrating both data protection and noise reduction:

<?php

class UserConnection {
    private string $username;
    private string $password; // Sensitive data
    private PDO $dbConnection; // Complex dependency
    private array $roles;

    public function __construct(string $username, string $password, PDO $db, array $roles) {
        $this->username = $username;
        $this->password = $password;
        $this->dbConnection = $db;
        $this->roles = $roles;
    }

    /**
     * Customize the debug output for var_dump()
     */
    public function __debugInfo(): array {
        return [
            'username' => $this->username,
            'password' => '********', // Mask the sensitive password
            'roles'    => $this->roles,
            // Exclude the complex $dbConnection object entirely
        ];
    }
}

// Example usage:
$pdo = new PDO('sqlite::memory:');
$user = new UserConnection('admin', 'super_secret_123', $pdo, ['editor', 'moderator']);

var_dump($user);

The Resulting Output

Without the __debugInfo() method, var_dump($user) would print the actual plain-text password and the entire internal structure of the PDO database connection object.

With the __debugInfo() method implemented, the output is clean, safe, and concise:

object(UserConnection)#2 (3) {
  ["username"]=>
  string(5) "admin"
  ["password"]=>
  string(8) "********"
  ["roles"]=>
  array(2) {
    [0]=>
    string(6) "editor"
    [1]=>
    string(9) "moderator"
  }
}

Important Considerations