PSR3

PSR-3, short for PHP Standards Recommendation 3, defines a standard logging interface for PHP libraries and applications. Published by the PHP Framework Interop Group (PHP-FIG), it aims to enable interoperable logging by ensuring that libraries can log messages in a consistent way regardless of the underlying logging implementation.

The core of PSR-3 is the LoggerInterface, named Psr\Log\LoggerInterface. It requires eight convenience methods—emergency(), alert(), critical(), error(), warning(), notice(), info(), and debug()—one for each severity level, plus a generic log($level, $message, array $context = array()) method. Implementations must accept a message string and an optional associative context array used for contextual data and message interpolation. The $level parameter in log() is expected to be one of the defined levels, typically as a string, though implementations may extend or map levels as needed.

Adoption and usage: By type-hinting dependencies on Psr\Log\LoggerInterface, code can work with any PSR-3 compliant logger. This promotes substitutability and reduces coupling between libraries and their logging backends. Many PHP logging libraries—most notably Monolog—provide PSR-3 compatible implementations, and major frameworks offer PSR-3 compatible adapters and services.

History and scope: PSR-3 is one of several PHP-FIG PSRs designed to standardize common interfaces. It has become a foundational component in PHP ecosystems, encouraging consistent logging practices across projects.