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SurveyJS
Open-Source JSON Form Builder to Create Dynamic Forms Right in Your App. With SurveyJS form UI libraries, you can build and style forms in a fully-integrated drag & drop form builder, render them in your JS app, and store form submission data in any backend, inc. PHP, ASP.NET Core, and Node.js.
For planning to multiclass, I would recommend this website https://5e.tools which is a great free resource for all kinds of 5e tabletop mechanics. You will be able to see what abilities your main class is going to get at higher levels, allowing you to plan a multiclass where you don’t miss out on them. Now it’s possible that Larian will make some of the high level abilities available sooner, they aren’t sticking to tabletop rules 100% but have been pretty faithful to them overall.