# rxfy \[The core package: atoms, lenses, models, and states] `rxfy` is the core package — the reactive primitives everything else builds on. It has no React dependency; [React Bindings](/react) consume these APIs through hooks. For the ideas behind them, start with [Core Concepts](/core-concepts). * [`createAtom`](/rxfy/create-atom) — the fundamental reactive cell: an `Observable` with synchronous `get()` / `set()` / `modify()`. * [`createLens`](/rxfy/create-lens) — a focused, two-way view into an Atom for reading and writing nested slices of state. * [`createModel`](/rxfy/create-model) — a typed entity descriptor plus the reactive `ModelStore` / `ModelRegistry` that hold live entities. * [`defineState`](/rxfy/define-state) — a typed, normalized state shape: fetch params, model fields (`array` / `single` / plain Zod values), and optional mutations. The SSR helpers (`dehydrate` / `hydrate` / `hydrationScript`) also ship in this package; they are documented with the full SSR story in [Server-Side Rendering](/core-concepts/ssr).