RAG-logger is an open-source logging tool designed for Retrieval-Augmented Generation (RAG) applications. It is a lightweight open-source alternative tailored to the specific logging needs of RAG, focusing on providing comprehensive logging features such as query tracking, retrieval result logging, LLM interaction logging, and step-by-step performance monitoring. It utilizes a JSON-based log format, supports daily log organization, automatic file management, and metadata enrichment. With its open-source, lightweight, and RAG-focused features, RAG-logger offers developers an effective tool for monitoring and analyzing the performance of RAG applications.