Logging in Kotlin: Best Libraries and Tools for Development

Logging in Kotlin: Overview of the Best Solutions

Logging is an essential part of any serious development, especially in a production environment. For Kotlin, as a language running on the JVM, all powerful Java logging libraries are available, but there are also specialized Kotlin solutions that take into account language features: null-safety, inline functions, coroutines, and extension functions. In this article, we will look at the best tools for logging in Kotlin — from classic to modern.

1. Why is the Right Library Choice Important?

Logging helps:

• Debug the application at runtime;
• Monitor errors and exceptions;
• Analyze performance;
• Collect metrics for auditing.

Poorly configured logging can slow down the application or, conversely, fail to provide necessary information. In Kotlin, it is important that the library works correctly with coroutines and does not create unnecessary overhead when using lambda expressions.

2. SLF4J — The Foundation of Modern Logging

SLF4J (Simple Logging Facade for Java) is not a library itself, but a facade (abstraction) over various implementations. In Kotlin, SLF4J is used everywhere, as it allows easy switching between Logback, Log4j 2, and other backends.

Usage example in Kotlin:

import org.slf4j.LoggerFactory

private val logger = LoggerFactory.getLogger(MyClass::class.java)

fun process(data: String) {    logger.info("Processing data: {}", data)    try {        // business logic    } catch (e: Exception) {        logger.error("Error processing data", e)    }}

Pros: versatility, support for parameterized messages (no string concatenation).
Cons: need to manually declare Logger in each class.

3. kotlin-logging — Idiomatic Kotlin Style

kotlin-logging is a wrapper over SLF4J that makes logging in Kotlin as concise and type-safe as possible. The library uses inline functions to minimize overhead.

Setup (Gradle):

implementation("io.github.microutils:kotlin-logging-jvm:3.0.5")

Usage example:

import mu.KotlinLogging

private val logger = KotlinLogging.logger {}

fun process(data: String) {    logger.info { "Processing data: $data" }    try {        // business logic    } catch (e: Exception) {        logger.error(e) { "Error processing data" }    }}

Features:

• Lazy evaluation of the message string (lambda is executed only if the logging level is enabled);
• Coroutine support — you can pass CoroutineName for contextual logging;
• Automatic class name detection via logger {}.

Cons: requires SLF4J + a backend (Logback/Log4j).

4. Logback — Industry Standard

Logback is the most popular implementation of SLF4J. Developed by the same author as Log4j 1.x, but significantly faster and more flexible. Supports asynchronous logging, file rotation, and conditional filters.

Example logback.xml configuration:

<configuration>    <appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">        <file>logs/app.log</file>        <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">            <fileNamePattern>logs/app-%d{yyyy-MM-dd}.log</fileNamePattern>            <maxHistory>30</maxHistory>        </rollingPolicy>        <encoder>            <pattern>%d{yyyy-MM-dd HH:mm:ss} [%thread] %-5level %l