TanStack Start

Full-stack React framework built on TanStack Router. Type-safe server functions via RPC, SSR/streaming, middleware composition, and deployment to Cloudflare Workers, Vercel, Netlify, AWS Lambda, and more.

RC: TanStack Start is currently in Release Candidate status. APIs may still change before the stable 1.0 release.

Package: @tanstack/react-start

Quick Reference

Pattern	Usage
createServerFn()	GET (default) — idempotent, cacheable data fetching
createServerFn({ method: 'POST' })	Mutations that change data
.inputValidator(zodSchema)	Input validation before handler
.handler(async ({ data }) => {})	Server-side logic with typed input data
getRequest()	Access full incoming Request inside handler/middleware
getRequestHeader(name)	Read a single request header by name
setResponseHeaders(headers)	Set outgoing response headers (caching, cookies)
useServerFn(fn)	Wrap server function for component use with pending state
createMiddleware().server(fn)	Request middleware for cross-cutting concerns
.middleware([dep])	Compose middleware with dependencies
next({ context: {} })	Pass data downstream through middleware chain
createMiddleware({ type: 'function' })	Function-level middleware with input validation
requestMiddleware in createStart()	Global middleware for all requests (SSR, fns, routes)
functionMiddleware in createStart()	Global middleware for server functions only
createIsomorphicFn()	Different implementations per environment
createServerOnlyFn()	Server-only utility — crashes if called from client
createClientOnlyFn()	Client-only utility — crashes if called from server
useSession()	Cookie-based session with encryption and secure settings
session.update()	Update session data
session.clear()	Clear session (logout)
beforeLoad	Auth check before route loads
_authenticated.tsx	Pathless layout route for grouped protection
throw redirect({ to: '/login' })	Redirect with return URL
await ensureQueryData()	Block SSR on critical data
prefetchQuery()	Start fetch, don't block SSR
<Suspense> boundaries	Define streaming chunks
head: ({ loaderData }) => ({})	Meta tags, Open Graph, favicons
head.scripts + JSON-LD	Structured data for LLMO (schema.org)
llms.txt server route	AI system guidance file
headers: () => ({...})	ISR / cache-control on route definition
server: { handlers: { GET, POST } }	API routes on createFileRoute
ssr: false	Disable SSR for specific routes (SPA mode)

Execution Boundaries

Function	Runs On	Client Can Call?	Use For
createServerFn()	Server	Yes (RPC stub)	Data fetching, mutations
createServerOnlyFn()	Server	No (throws)	Secrets, DB connections
createClientOnlyFn()	Client	N/A	localStorage, DOM APIs
createIsomorphicFn()	Both	N/A	Per-environment implementations

Deployment (Vite Plugins)

Platform	Plugin	Runtime
Cloudflare	@cloudflare/vite-plugin	Workers
Netlify	@netlify/vite-plugin-tanstack-start	Node
Vercel	nitro/vite (preset: 'vercel')	Node
Node.js/Docker	nitro/vite (preset: 'node-server')	Node
AWS Lambda	nitro/vite (preset: 'aws-lambda')	Node
Bun	nitro/vite (preset: 'bun')	Bun
Static	nitro/vite (preset: 'static')	None

Common Mistakes

Mistake	Fix
No .inputValidator() on server functions	Always validate with Zod schemas
Raw fetch instead of createServerFn	Loses type safety, serialization, and code splitting
Mixing server/client code without boundaries	Use createServerOnlyFn / createClientOnlyFn
Checking auth in every handler	Use middleware composition or beforeLoad
Awaiting all data in loader	Only await critical data, prefetch the rest
Date.now() in render	Pass timestamp from loader (hydration mismatch)
Missing nodejs_compat flag	Required in wrangler.toml for Cloudflare
GET for mutations	Use POST for create/update/delete
Cookies not forwarded to external APIs	Use getRequestHeader() or createIsomorphicFn
process.env in loader (runs on both)	Wrap in createServerFn — loaders run client-side too
Unvalidated server env vars	Validate with Zod in .server.ts files
Storing auth tokens in localStorage	Use HTTP-only cookies via useSession
Exposing raw DB errors to client	Catch and return user-friendly messages, log details
No structured data for content pages	Add JSON-LD via head.scripts for AI discoverability

Delegation

Use this skill for TanStack Start server functions, middleware, SSR/streaming, route protection, API routes, and deployment configuration. Delegate to tanstack-router for file-based routing, search params, and data loading patterns. Delegate to tanstack-query for cache management, optimistic updates, and query patterns.

If the tanstack-form skill is available, delegate form state management, validation, and field patterns to it. If the local-first skill is available, delegate local-first architecture decisions and sync engine selection to it. If the electricsql skill is available, delegate ElectricSQL shapes, auth configuration, and write patterns to it. If the tanstack-db skill is available, delegate reactive collections, live queries, and optimistic mutation patterns to it.

References

• Server Functions — createServerFn, useServerFn, validation, auth, request context, response headers, file uploads, streaming, TanStack Query integration
• Middleware — composition, function-level middleware, route-level middleware, global middleware, logging, rate limiting
• SSR and Streaming — Suspense, prerendering, ISR, cache-control, hybrid strategies, hydration safety
• Route Protection — beforeLoad, pathless layouts, session security, login/logout, header forwarding, Better Auth
• API Routes — server handlers, REST patterns, route-level middleware, webhooks, health check, server functions vs server routes
• Deployment — Vite plugins, adapter comparison, Cloudflare D1/KV/R2 bindings, Docker, prerendering
• SEO and Head Management — head property, meta tags, Open Graph, Twitter Cards, favicons, SEO helper
• LLM Optimization (LLMO) — JSON-LD structured data, schema.org, llms.txt, machine-readable endpoints, AI citation patterns
• Error Handling — discriminated unions, custom error classes, status codes, result types vs try-catch
• File Organization — entry points, plugin config, execution boundaries, env validation, .server.ts convention
• Known Issues — 10 documented issues with workarounds
• Query Integration — Router+Query setup, SSR integration, setupRouterSsrQueryIntegration, DevTools
• Integration Flows — form submission with cache update, infinite scroll, paginated tables, auth-protected routes, error handling
• Local-First Integration — shape proxy server functions, mixing server-based and local-first data, ElectricSQL deployment
• Electric Middleware — auth middleware for shape proxies, global middleware config, sendContext, function-level validation