Why TanStack Start

Verified against @tanstack/react-start v1.168.x — July 2026.

What it is

TanStack Start is a full-stack React framework built on top of TanStack Router, running on Vite. You get file-based routing, server-side rendering, streaming, and server functions (isomorphic RPC calls) — the same category of tool as Next.js or Remix.

The difference is philosophy, not feature count.

The core difference

Next.js’s App Router treats the server as the owner of your component tree. Your components run there by default, and the client is where you opt in to interactivity ('use client').

TanStack Start flips that. The router owns the app. Server rendering, data loading, and (optionally) server components are things the router does for a route, not a mode the whole app lives in. Every route decides for itself how much of it runs on the server — see selective SSR for the actual mechanism (ssr: true, 'data-only', false).

graph TD
    subgraph "Next.js App Router"
        A1[Server owns the tree] --> A2["'use client' opts OUT to the client"]
    end
    subgraph "TanStack Start"
        B1[Router owns each route] --> B2["Each route opts IN to server rendering, deferred data, or RSC"]
    end

Practically, this means Start doesn’t ask you to buy into one rendering model for the whole app. A dashboard can SSR its shell and client-render a live-data widget in the same route tree, with no framework-level ceremony — just a per-route config value.

The primitive you’ll use everywhere: server functions

Almost everything in this book builds on one idea: a function that’s defined once, runs on the server, and is called like a normal async function from anywhere — a loader, a component, another server function.

src/server/get-user.ts

import { createServerFn } from '@tanstack/react-start'
import { z } from 'zod'

export const getUser = createServerFn({ method: 'GET' })
  .validator(z.object({ id: z.string() }))
  .handler(async ({ data }) => {
    // this code never ships to the browser
    return db.user.findUnique({ where: { id: data.id } })
  })

Call it from a route loader (getUser({ data: { id } })) or from a client component via useServerFn(getUser). The framework compiles the server body out of the client bundle automatically — you don’t write two versions of this function. Part 3 covers this in depth.

When to reach for Start

• You want React with real SSR/streaming, but don’t want Next.js’s server-first conventions dictating your whole architecture.
• You’re comfortable owning your Vite config and want a framework that stays close to it, rather than replacing it.
• You want to add server rendering incrementally to specific routes, not as an all-or-nothing switch.

If you want a mature, batteries-included RSC-first framework today, Next.js is further along on that specific axis — Start’s RSC support is real but still experimental (Part 9, Appendix A). If you want isomorphic server functions and fine-grained per-route rendering control on a Vite-native stack, Start is built for exactly that.