This document introduces Padrino::Validation::HTML5, a Padrino plugin that injects HTML5 form validations from ActiveModel validations. It allows writing validations in the model and view similarly to ActiveModel, and renders the appropriate HTML5 validation attributes. Links are provided to Padrino and HTML5 validation rule resources. The document encourages translation and ends with an invitation to an underground Padrino event in Kyoto.