Build your first API Specification with API Designer | Getting Started with MuleSoft

I quite like using the guided mode to do the creation of the data types and to sketch out the API, then jump into the text-IDE form of API designer. I find that means you get ease of creation and then get to do more advanced things than the GUI mode allows.. But it is abone way journey as you can't go back to the GUI mode once you have edited RAML or OAS.