Critical rules: never touch window/localStorage at loader top level (loaders run on the server too) — gate with ssr: false/'data-only' or useEffect instead; share one queryOptions factory between ensureQueryData (loader) and useQuery (component) so cache keys match; prefetch through the router-context queryClient, never a new one; invalidate loaders/Query cache after every server-function write; and remember ssr only tightens down the route tree, a child can never loosen a parent's ssr: false back to true.

Includes templates for a Query-prefetching route and a selective-SSR route.

Do NOT use this skill for generic TanStack Router/Query API questions — route trees, search params, useQuery/useMutation basics belong to react-expert's react-tanstack-router skill.

TanStack Start — Routing Data

Agent Workflow (MANDATORY)

Before ANY implementation, spawn in parallel:

1. fuse-ai-pilot:explore-codebase — map src/routes/, existing loaders, router.tsx, queryClient wiring
2. fuse-ai-pilot:research-expert — verify Start API via Context7 /websites/tanstack_start_framework_react
3. mcp__context7__query-docs — confirm loader / ssr / ensureQueryData signatures