GCViewer is a mature, monolithic Java desktop application (Swing GUI) and CLI tool for parsing, analyzing, and visualizing garbage collection (GC) logs from a wide range of JVM implementations (Sun/Oracle, IBM, HP, BEA/JRockit, Go, and modern OpenJDK unified logging). Its architecture follows a layered pattern: a family of DataReader implementations parse vendor-specific log formats into a unified GCModel of GC events. This model is then consumed by statistical analysis utilities (DoubleData, RegressionLine) and rendered via Swing charts or exported to CSV/PNG/plain text. The codebase demonstrates strong engineering in its utility classes (NumberParser, HttpUrlConnectionHelper, MonitoredBufferedInputStream) and test infrastructure (extensive real-world log fixtures). However, it suffers from significant technical drift, primarily a Java 8 baseline, alongside accumulated technical debt such as e.printStackTrace() usage, ignored tests, known export bugs, and fragile parser logic. It is actively maintained but carries the weight of supporting two decades of JVM GC log formats.