How to Define a Custom Logging Formatter

Each logging handler uses a Formatter to format the record before logging it. All Monolog handlers use an instance of Monolog\Formatter\LineFormatter by default but you can replace it. Your formatter must implement Monolog\Formatter\FormatterInterface.

For example, to use the built-in JsonFormatter, register it as a service then configure your handler to use it:

  • YAML
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    # config/packages/prod/monolog.yaml (and/or config/packages/dev/monolog.yaml)
monolog:
    handlers:
        file:
            type: stream
            level: debug
            formatter: 'monolog.formatter.json'
  • XML
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    <!-- config/services.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:monolog="http://symfony.com/schema/dic/monolog"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/monolog
        https://symfony.com/schema/dic/monolog/monolog-1.0.xsd">

    <!-- config/packages/prod/monolog.xml (and/or config/packages/dev/monolog.xml) -->
    <monolog:config>
        <monolog:handler
            name="file"
            type="stream"
            level="debug"
            formatter="monolog.formatter.json"
        />
    </monolog:config>
</container>
  • PHP
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    // config/services.php
use Monolog\Formatter\JsonFormatter;

// config/packages/prod/monolog.php (and/or config/packages/dev/monolog.php)
$container->loadFromExtension('monolog', [
    'handlers' => [
        'file' => [
            'type'      => 'stream',
            'level'     => 'debug',
            'formatter' => 'monolog.formatter.json',
        ],
    ],
]);