📡 Skill: tanstack-query-expert (v1.0.0)

Executive Summary

Senior Server State Architect for TanStack Query v5 (2026). Specialized in reactive data fetching, advanced caching, and high-performance integration with React 19 and Next.js 16. Expert in eliminating waterfalls, managing complex mutation states, and leveraging platform-level caching via Next.js "use cache" and Partial Prerendering (PPR).

📋 The Conductor's Protocol

1. Architecture Choice: Determine if data fetching should happen in RSC (via React 19 use hook + "use cache") or on the client (via TanStack Query).
2. Hydration Strategy: For SSR/PPR, always prefetch on the server and use HydrationBoundary to ensure instant client-side data availability.
3. Mutation Tracking: Use useMutationState to handle global loading/pending states without prop drilling.
4. Verification: Use TanStack Query Devtools v5 to audit query states, stale times, and cache invalidation.

🛠️ Mandatory Protocols (2026 Standards)

1. The "Object Syntax" Rule

TanStack Query v5 ONLY supports the object-based syntax for all hooks.

• Rule: Never use the deprecated positional argument syntax (e.g., useQuery(key, fn)).
• Correct: useQuery({ queryKey: [...], queryFn: ... }).

2. React 19 & Next.js 16 Integration

• PPR First: Wrap client components using TanStack Query in <Suspense> to allow Next.js 16 to stream content while serving the static shell.
• "use cache" Directive: For server-side prefetching, utilize Next.js 16's "use cache" to cache the prefetch results at the platform level.
• Action Mutations: Prefer React 19 Actions for simple form mutations; use TanStack Query mutations for complex state, optimistic updates, and background refetching.

3. Cache & Performance Hardening

• Stale Time: Default to at least 5000 (5s) to prevent excessive refetching.
• GC Time: Use gcTime (renamed from cacheTime in v5) to manage memory cleanup.
• Query Keys: Always use stable, array-based query keys. Treat keys as unique identifiers for your data.

🚀 Show, Don't Just Tell (Implementation Patterns)

Quick Start: Modern Query with Suspense (React 19)

"use client";

import { useSuspenseQuery } from "@tanstack/react-query";
import { queryOptions } from "@tanstack/react-query";

// Pattern: Reusable Query Options
export const userOptions = (id: string) => queryOptions({
  queryKey: ["users", id],
  queryFn: async () => {
    const res = await fetch(`/api/users/${id}`);
    if (!res.ok) throw new Error("Failed to fetch");
    return res.json();
  },
  staleTime: 1000 * 60 * 5, // 5 min
});

export function UserProfile({ id }: { id: string }) {
  // Guaranteed data availability via Suspense
  const { data: user } = useSuspenseQuery(userOptions(id));

  return <div>Welcome, {user.name}</div>;
}

Advanced Pattern: Global Mutation Tracking

import { useMutationState } from "@tanstack/react-query";

function PendingUploads() {
  const pendingVariables = useMutationState({
    filters: { status: "pending", mutationKey: ["upload"] },
    select: (mutation) => mutation.state.variables as { fileName: string },
  });

  return (
    <ul>
      {pendingVariables.map((vars, i) => (
        <li key={i} className="opacity-50 italic text-blue-400">
          Uploading {vars.fileName}...
        </li>
      ))}
    </ul>
  );
}

🛡️ The Do Not List (Anti-Patterns)

1. DO NOT use onSuccess, onError, or onSettled in useQuery. They are removed in v5. Use useEffect or move logic to queryFn.
2. DO NOT ignore isPending. It replaced isLoading in v5 for "no data yet" states.
3. DO NOT use useQuery without a queryKey. It's the only way to manage the cache effectively.
4. DO NOT forget to await prefetchQuery on the server. Non-awaited prefetches lead to hydration mismatches.
5. DO NOT use enabled with useSuspenseQuery. It's incompatible with the guarantee of data presence.

📂 Progressive Disclosure (Deep Dives)

• [v5 Migration & Breaking Changes](./references/migration.md): Moving from v4 to v5 safely.
• [Next.js 16 SSR & Hydration](./references/ssr-hydration.md): Prefetching, HydrationBoundary, and "use cache".
• [Advanced Mutations & Optimistic UI](./references/mutations.md): useMutationState and simplified v5 patterns.
• [Performance & Infinite Queries](./references/performance-infinite.md): maxPages and bi-directional pagination.

🛠️ Specialized Tools & Scripts

• scripts/audit-query-keys.ts: Checks for non-array query keys or unstable key generation.
• scripts/generate-query-hook.py: Boilerplate generator for v5 query/mutation pairs.

🎓 Learning Resources

• TanStack Query Docs
• TkDodo's Blog (Maintainer)
• React 19 Data Fetching Guide

Updated: January 23, 2026 - 16:45