Pareto 3.0: A Lightweight React SSR Framework, Rebuilt on Vite 7

TL;DR: Pareto 3.0 is a ground-up rewrite — Rspack replaced by Vite 7, React 19 required, simplified routing conventions, Immer-powered state management, and a new ParetoErrorBoundary component. Try it: npx create-pareto@latest my-app

If you've used Next.js or Remix, you know the React SSR patterns: file-based routing, layouts, loaders, streaming. Pareto gives you the same patterns without the complexity. No server components, no framework lock-in, no config maze.

Pareto 3.0 is the release where the framework caught up with the vision: everything you need to build fast React apps, nothing you don't.

What changed in 3.0

Vite 7 replaces Rspack

Pareto 2.x used Rspack with separate client/server configs, Babel, and a lazy compiler. All gone.

Pareto 3.0 uses Vite 7:

• Instant dev server — ready in milliseconds, not seconds
• Native ESM — no bundling during dev
• React Fast Refresh — HMR that preserves component state
• Your Vite plugins work — PostCSS, Tailwind, MDX, etc. No framework wrappers
• One config — configureVite() in pareto.config.ts

// pareto.config.ts
import type { ParetoConfig } from '@paretojs/core'

const config: ParetoConfig = {
  configureVite(config) {
    config.plugins.push(myVitePlugin())
    return config
  },
}

export default config

React 19

Pareto 3.0 requires React 19. You get use(), Actions, useOptimistic(), and improved Suspense — but no server components. Pareto uses the loader pattern: your components are standard React that works on both server and client.

Simplified routing

Convention files in 3.0:

New: loader.ts — Define loaders in a separate file. Keeps data fetching separate from components:

// app/dashboard/loader.ts
import type { LoaderContext } from '@paretojs/core'

export function loader(ctx: LoaderContext) {
  return { stats: getDashboardStats() }
}

Changed: Error handling — error.tsx convention is gone. Use ParetoErrorBoundary instead — place it anywhere in the component tree:

import { ParetoErrorBoundary } from '@paretojs/core'

<ParetoErrorBoundary fallback={({ error }) => <p>{error.message}</p>}>
  <RiskyComponent />
</ParetoErrorBoundary>

State management with Immer

defineStore() now uses Immer. Mutate directly, get immutable results:

import { defineStore } from '@paretojs/core/store'

const counterStore = defineStore((set) => ({
  count: 0,
  increment: () => set((draft) => { draft.count++ }),
}))

// Use anywhere — supports direct destructuring
const { count, increment } = counterStore.useStore()

SSR serialization is automatic — no hydration code needed.

Security headers

OWASP-recommended headers out of the box:

import { securityHeaders } from '@paretojs/core/node'

app.use(securityHeaders())

Streaming SSR — the killer feature

The reason Pareto exists. Send the page shell immediately, stream slow data as it resolves:

import { defer, useLoaderData, Await } from '@paretojs/core'
import { Suspense } from 'react'

export function loader() {
  return defer({
    quickData: { total: 42 },           // sent immediately
    slowData: fetchFromDatabase(),       // streamed later
  })
}

export default function Page() {
  const { quickData, slowData } = useLoaderData()

  return (
    <div>
      <h1>{quickData.total} items</h1>
      <Suspense fallback={<Skeleton />}>
        <Await resolve={slowData}>
          {(data) => <DataTable rows={data} />}
        </Await>
      </Suspense>
    </div>
  )
}

Users see content fast. Slow data loads progressively. No full-page spinners.

Migration from 2.x

1. Install @paretojs/core@3, update to React 19
2. Remove Rspack config, use configureVite() instead
3. Replace error.tsx files with ParetoErrorBoundary
4. Test loaders with Vite's dev server

Try it

npx create-pareto@latest my-app
cd my-app
npm install
npm run dev

Open http://localhost:3000. Edit app/page.tsx. Done.

Links:

• GitHub: childrentime/pareto
• Docs: paretojs.dev
• Full release notes: paretojs.dev/blog/pareto-3/

Pareto is MIT licensed and open source. If you find it useful, give it a star on GitHub.