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:

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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'

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<!-- config/packages/prod/monolog.xml (and/or config/packages/dev/monolog.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">

    <monolog:config>
        <monolog:handler
            name="file"
            type="stream"
            level="debug"
            formatter="monolog.formatter.json"
        />
    </monolog:config>
</container>

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// config/packages/prod/monolog.php (and/or config/packages/dev/monolog.php)
use Symfony\Config\MonologConfig;

return static function (MonologConfig $monolog): void {
    $monolog->handler('file')
        ->type('stream')
        ->level('debug')
        ->formatter('monolog.formatter.json')
    ;
};

Many built-in formatters are available in Monolog. A lot of them are declared as services and can be used in the formatter option:

• monolog.formatter.chrome_php: formats a record according to the ChromePHP array format
• monolog.formatter.gelf_message: serializes a format to GELF format
• monolog.formatter.html: formats a record into an HTML table
• monolog.formatter.json: serializes a record into a JSON object
• monolog.formatter.line: formats a record into a one-line string
• monolog.formatter.loggly: formats a record information into JSON in a format compatible with Loggly
• monolog.formatter.logstash: serializes a record to Logstash Event Format
• monolog.formatter.normalizer: normalizes a record to remove objects/resources so it's easier to dump to various targets
• monolog.formatter.scalar: formats a record into an associative array of scalar (+ null) values (objects and arrays will be JSON encoded)
• monolog.formatter.wildfire: serializes a record according to Wildfire's header requirements