When working with TanStack Query in React, the Devtools extension is an essential companion for understanding and debugging your application's data fetching layer. The TanStack Query Devtools provide a visual interface directly in your browser, allowing you to:

• Inspect the state of all queries and mutations;
• Monitor cache contents;
• Observe how data flows and updates in real time as you interact with your app.

To install the Devtools, add the package via npm with npm install @tanstack/react-query-devtools and then include the ReactQueryDevtools component somewhere in your React component tree, typically near the root. Once integrated, you will see a toggle button in your app that opens the Devtools panel, giving you access to all its features.

With the Devtools open, you can walk through the active queries and view detailed information about each one. The panel lists all queries currently in memory, showing their keys, statuses (such as "idle", "loading", "success", or "error"), and when they were last fetched. By selecting a query, you can drill down into its data, see the exact query key, and inspect metadata like fetch status, cache time, and observers. The Devtools also let you view the cached data for any query, which is especially helpful for checking whether your data is current or stale. If you are using mutations, you can inspect their status and results in a similar way, making it much easier to debug update flows and server interactions.

Tips for Identifying and Resolving Common Issues Using Devtools

• Check query statuses in the Devtools to confirm whether data is "loading", "success", or "error";
• Inspect cached data for each query to verify if the information is up to date or stale;
• Use the Devtools to manually refetch or remove queries from the cache when troubleshooting data synchronization issues;
• Review mutation statuses and results to debug problems with data updates or server communication;
• Monitor cache times and invalidation events to understand why data is not refreshing as expected.

Using these features, you can quickly diagnose and resolve most data-fetching and caching issues in your React application with TanStack Query.