If you're curious whether a website is built using React.js, there are several ways you can check—ranging from quick and easy browser tricks to more technical inspection methods. Here's how you can do it:

1. Use React Developer Tools (Browser Extension)

Best Method for Accuracy

• Install the React Developer Tools extension: Chrome Web Store Firefox Add-ons

Once installed:

• Visit the website you want to check.
• Open your browser DevTools (right-click > Inspect or Ctrl + Shift + I).
• Look for a React tab.
• If it’s there, and you can see the component tree, the site is almost certainly built with React.

2. Check the Page Source or DevTools (Manually)

Even without the extension, you can look for signs:

• Right-click > Inspect
• Open the Console tab
• Type:  !!window.React || !!window.__REACT_DEVTOOLS_GLOBAL_HOOK__

If it returns true, React is likely being used.

You can also look for:

• HTML elements with class names like react-root, App, jsx-*
• References to react.js or react-dom.js in the page's scripts

3. Use Online Tools

There are websites that scan and tell you what technologies a site is using:

• https://www.wappalyzer.com/
• https://builtwith.com/

Just enter the URL (e.g., flipfilezone.com) and it'll tell you if React is in the stack.

4. Look at Network Requests

Go to the Network tab in DevTools and reload the page.

• Look for files like main.js, bundle.js, or anything from a tool like Webpack or Vite.
• If you see files with react, jsx, or vite in their names or headers, it’s another strong clue.

Example: File Conversions | Flip File Zone

My friend built flipfilezone.com using React with a Django back-end. If you inspect it with React DevTools or check the scripts, you’ll see React in action—especially in the dynamic user interface and components like modals, buttons, and real-time indicators.