What is VSN

VSN, pronounced Vision, is a lightweight framework for adding interactivity to server-rendered pages without replacing your HTML. It treats your existing markup as the source of truth and layers behavior on top of it using CFS (Cascade Functioning Sheets).

Why it exists

Most JS frameworks assume the browser owns the UI. VSN.js flips that model: your backend renders the page, and VSN.js enhances it in-place. That keeps SEO strong, page loads fast, and your markup readable.

The VSN mental model

Behavior tree: behaviors are scoped to selectors, like CSS.
Scope cascade: state flows down the DOM tree.
Small runtime: no virtual DOM, no client-side templating.

When to use it

Use VSN.js when you want interactive UI on top of your important SSR SEO pages:

E-commerce
Landing Pages
Marketing
CMS
Documentation

If you need a full client-side app with heavy routing and state, VSN.js is probably not the right tool.

Notes from the creator

Who said all the good ideas have already been thought of?