query

Server data is not application state, but almost everyone stores it that way. TanStack Query fixes that: it handles caching, background refetching, request deduplication, pagination, and knowing when data went stale, so you stop writing the same useEffect plus loading plus error triangle in every component. MIT licensed, with adapters for React, Vue, Svelte, Solid, and plain JS.

It is protocol agnostic, which matters more than it sounds. Query does not care whether you fetch over REST, GraphQL, tRPC, or a promise you wrote by hand. You hand it a key and a function and it owns the rest. The devtools panel alone earns the install, because watching cache entries go stale and refetch in real time is usually where the bug turns out to be.

Nothing to run and nothing to pay. It lives in your bundle. The cost is conceptual: query keys are a cache namespace, and getting them wrong produces stale data that reads like a backend bug. Spend an afternoon on key structure before spreading it across an app.

The catch is that Query is not a state manager and people keep using it as one. Client state, form state, and UI state still need their own answer. Keep Query on the server-data side of that line.