MJML is a markup language designed to reduce the pain of coding a responsive email. Its semantic syntax makes it easy and straightforward while its rich standard components library fastens your development time and lightens your email codebase. MJML's open-source engine takes care of translating the MJML you wrote into responsive HTML.
One of the great advantages of MJML is that it's component based. Components abstract complex patterns and can easily be reused. Added to the standard library of components, it is also possible to create your own components!
To learn how to create your own component, follow this step-by-step guide which also includes a ready-to-use boilerplate.