An Overview of Log Levels

Eva Claes
Technical Copywriter
January 08, 2024

In the landscape of software development and maintenance, logging stands as a pivotal practice, acting as a beacon in the often turbulent seas of debugging and system analysis. By creating a chronicle of events and states within an application, logs offer developers and system administrators a tangible narrative that can be used to unravel the complex tales of both successes and failures in system processes. Enter the concept of log levels – a means to bring order and priority to the potential cacophony of log messages.

Log levels are an effective tool for categorizing these messages based on their severity and the attention they demand. They enable teams to sift through vast quantities of log data and isolate the signals of importance from the noise. This article delves deep into the hierarchy of log levels, from the granular tracing messages to high-severity error alerts. Our journey will clarify what these levels entail, providing insights into their effective application and revealing how they serve as indispensable allies in diagnosing and resolving application problems. Whether you're a seasoned developer or an operations specialist, understanding and utilizing log levels is a crucial skill that can dramatically enhance your debugging prowess and operational oversight.

The Basics of Logging

Logging is the systematic practice of recording events and data points that occur within a software application. This trail of breadcrumbs is not just a debugging tool; it is the historical record of the application’s life as it interacts with users, interfaces with other systems, and encounters both triumphs and trials. At its core, a log entry typically encapsulates several pieces of information: a timestamp marking the exact or relative time of the event, a log level denoting the severity, and a message providing context or details about the event. Optionally, log entries may include other details like the user ID, process ID, or stack trace.

In its essence, logging serves as an application’s diary, and as with any journal, the insights gleaned from it are largely dependent on the consistency and clarity of the entries made. Across the IT industry, various log aggregation and monitoring tools exist to parse, sort, and visualize these logs, thereby providing an analysis platform. Tools like Elasticsearch, Splunk, or Graylog come with powerful features to digest this data and offer real-time monitoring and alerting capabilities.

The real power of logging shines through when it is implemented thoughtfully, with a clear understanding of what data is valuable to record. Over-logging can lead to an excess of data, making it difficult to identify key events, while under-logging may mean missing out on critical information during an application crisis. Thus, the practice of logging is as much about what you log as it is about what you choose to omit. The use of log levels is the primary means by which developers and system administrators calibrate this balance, ensuring that the log data is both manageable and meaningful.

Overview of log levels

Log levels form a hierarchical value system that categorizes log entries according to their urgency and relevance to different stakeholders, making log analysis more efficient. Predominantly, there are six widely recognized log levels that developers and system operators use to triage and interpret logged information. Arranged in order of increasing severity, these levels are:

  • TRACE: The lowest level, providing detailed information mostly useful for developers when debugging.
  • DEBUG: Offers granular operational details that are helpful during development and debugging phases.
  • INFO: General messages indicating that the application is running as expected.
  • WARN: Acts as a heads-up for potential issues that warrant attention but haven't caused an error yet.
  • ERROR: Highlights problems that have a detrimental effect on application operation.
  • FATAL/EMERGENCY: Marks very severe error events that typically lead the application to abort.

Each level serves a distinct purpose, allowing teams to sort and address the multitude of messages produced by a running application conscientiously.

Detailed Explanation of Each Log Level


The TRACE log level is the most detailed and verbose, providing a microscopic view of what is happening in your application. It's typically used during development to record the flow through the code, variable values, and to understand the execution path. The amount of information TRACE logs generate can be overwhelming, so it's usually only enabled when you need to diagnose an elusive bug or want insight into the application's behavior during a very specific time frame.


DEBUG logs are a notch below TRACE in terms of verbosity and are essential during the development and debugging phases. They contain information useful to developers, like the state of the application, the execution steps, or the values of variables right before an issue occurs. By analyzing DEBUG logs, developers can more readily pinpoint the root cause of a problem. This log level is too verbose for production environments but can be enabled temporarily to gather detailed information needed to debug a particularly tricky issue.


The INFO log level conveys general operational messages that demonstrate the application is working as expected. It's the gold standard for routine logging and is often used to signal the start and end of application processes, successful completion of significant transactions, or configuration details at startup. INFO logs provide a good balance of detail and conciseness, offering a broad picture of system health and behavior without the minutiae of debug-level logs. They are immensely useful for system administrators and support personnel for routine monitoring tasks.


Logs at the WARN level denote potentially harmful situations that may not immediately disrupt functionality but require attention. These could include non-critical issues, deprecated API usage, or anything that signals a deviation from ideal performance. A WARN log doesn't indicate an error but suggests that if the warning is not heeded, it might elevate to a more severe error or affect system performance. By monitoring WARN logs, developers and system administrators can proactively address problems before they escalate.


The ERROR log level captures serious issues that affect the program's execution but do not necessarily cause a complete halt. These logs are critical for troubleshooting as they provide insight into runtime errors, such as exceptions that could not be handled or problems encountered during the execution of a task. Through ERROR logs, you can trace back to the conditions that caused the fault and take corrective measures to ensure system stability.


At the FATAL log level, you're dealing with critical problems that cause your application to abort. These logs signify an unrecoverable error that has led or will lead to a system crash or a significant disruption in service. Fatal conditions often require immediate attention, as they impact the steady-state and continuity of the application. Examples might include a failed initialization of a critical component or an unhandled exception in the core workflow. FATAL logs are typically examined as part of post-mortem analyses to prevent a recurrence of the event that caused them.


Although not always distinct in every logging framework, the EMERGENCY log level is sometimes employed to indicate system-wide catastrophe or an imminent shutdown. These logs represent the highest priority, making them essential for alerts that need to escalate straight to system administrators or trigger automated system recovery procedures. EMERGENCY log entries could denote catastrophic failures where the application has not only stopped working but might also be affecting other interconnected systems or services, requiring an immediate and coordinated response to the situation.

Note that not all logging systems differentiate EMERGENCY from FATAL. In some frameworks, the FATAL level may be considered the highest, serving a similar purpose. However, when EMERGENCY is recognized, it should be reserved for truly system-critical issues.

Best Practices for Log Levels

In the nuanced world of application logs, it is crucial to discern the appropriate log level for any given message to maintain clarity and usefulness. As a guiding principle, developers should consider the intended audience and the message's urgency. For example, DEBUG logs are meant for developers during the troubleshooting process, so they should contain detailed information helpful in debugging, while INFO logs target system administrators monitoring the application's health and should provide a clear picture of its normal operation.

A strategically planned log level hierarchy is instrumental in ensuring log data serves its purpose without overwhelming the system or the teams involved. Regularly reviewing and updating logging practices can prevent logs from becoming a source of noise rather than a resource. For instance, use WARN to alert users of deprecations or suboptimal operations that do not require immediate action, while ERROR should be reserved for significant issues that demand attention. Using log levels consistently helps in filtering and searching through log data more effectively when issues arise.

Avoiding common logging pitfalls is equally essential. Over-logging, which happens when too much data is logged, can lead to performance issues and difficulty finding relevant information. To combat this, periodically audit what is being logged at each level and ensure that it aligns with the defined purpose of that level. Under-logging, on the other hand, fails to provide enough information for diagnosing issues and should be addressed by ensuring that all significant actions in the application are logged at an appropriate level. Also, ensure that log messages are meaningful and include enough context to be understood on their own, which often means including identifiers and state information relevant to the log event.


In conclusion, understanding and effectively using log levels are essential for maintaining smooth application operations and efficient troubleshooting. From TRACE for in-depth debugging to FATAL for capturing critical system failures, each log level serves a distinct purpose in the hierarchy of log severity. By applying best practices in log level usage, developers and system administrators can ensure their logs are informative, actionable, and manageable. Incorporating sophisticated log management strategies within the development lifecycle not only streamlines debugging but also enhances overall application reliability. Remember, logs are your silent sentinels in the digital realm; by mastering their levels, you gain insight and control over your IT systems, paving the way for improved performance and a better end-user experience.