The Spring Petclinic is the canonical reference sample application built with Spring Boot and Thymeleaf, demonstrating best practices in building Spring-based web applications; forks also exist showcasing implementations with modern architectures like microservices, reactive stacks, and AI integrations. In its default configuration, Petclinic uses an in-memory database (H2) which gets populated at startup with data. The h2 console is exposed and it is possible to inspect the content of the database using the jdbc:h2:mem:<uuid> URL. The UUID is printed at startup to the console. One of the best parts about working on the Spring Petclinic application is that we have the opportunity to work in direct contact with many Open Source projects.