Loglevels

Loglevels, or log levels, refer to a categorization scheme used by logging systems to indicate the severity or importance of a message. The level determines whether the message should be recorded and how prominently it should be treated. By grouping messages, loglevels allow operators to control verbosity and focus on relevant information in different environments such as development or production.

Common levels, from most verbose to least, include TRACE or DEBUG for detailed troubleshooting, INFO for general runtime information, WARN or WARNING for situations that are unusual but not necessarily errors, ERROR for recoverable or non-fatal problems, and FATAL or CRITICAL for severe failures. Some frameworks introduce additional levels or reuse synonyms; the exact names and ordering can differ, but the intent remains the same: higher-severity levels filter out lower-severity messages.

Configuration typically sets a threshold: messages with a level at or above the threshold are emitted, while lower-severity messages are suppressed. The log messages can be written to console, files, or centralized systems, and may be routed differently depending on the level.

Best practices: start with a sensible default (often INFO or WARN), enable more verbose levels like DEBUG only in development or on specific components, avoid logging sensitive data, use structured or contextual logging, include identifiers to correlate events, and periodically review emitted logs to tune levels and avoid flood.

Loglevels are a common feature across programming languages and frameworks, including Java, Python, and JavaScript ecosystems, though concrete implementations vary. They provide a simple, flexible mechanism for controlling log output and supporting operational monitoring and troubleshooting.