VizTracer is a low-overhead Python tool for tracing, debugging, and profiling code execution, offering detailed function entry/exit timelines with source code. It requires no source code changes for most features and has no package dependencies. VizTracer supports threading, multiprocessing, subprocesses, async, and PyTorch, with a powerful front-end powered by Perfetto that can smoothly render large traces. It works across Linux, macOS, and Windows. Key features include trace filtering, custom event logging, and support for Jupyter notebooks. Installation is via pip, and it can be used via command line, inline scripts, or a VS Code extension. VizTracer is optimized for performance, with minimal overhead, and supports advanced use cases like remote attach and flamegraphs.