MedRAX is a versatile AI agent for medical reasoning on chest X-rays. It leverages GPT-4o with vision capabilities as the backbone LLM and integrates state-of-the-art CXR analysis tools through LangChain and LangGraph frameworks. The system dynamically routes between tools to address complex medical queries without additional training. A companion benchmark called ChestAgentBench contains 2,500 complex medical queries across 7 categories for evaluation.