What is React?

What React does

A React app is a tree of components: functions that take data and return what to display, written in JSX, which looks like HTML inside JavaScript.

function Price({ amount }) {
  return <p className="price">{amount} EUR</p>;
}

When data changes, React works out what changed and updates only that part of the page.

What React does not do

React is a library, not a full framework. On its own it does not provide routing, data fetching, server rendering, a build setup or deployment. React's own documentation recommends starting new apps with a framework, such as Next.js or React Router, or with a build tool such as Vite.

Why it is everywhere

• A huge ecosystem of components, libraries and tutorials.
• It is the default output of many AI app builders and code assistants.
• React Native uses the same model for mobile apps.

Client-side React and SEO

A React app built only for the browser sends an almost empty HTML page and builds the content with JavaScript. Google can render JavaScript, but rendering may be delayed, and other crawlers, link preview bots and some AI crawlers often read only the initial HTML. Titles, descriptions and Open Graph tags set from JavaScript may be missed entirely.

• For pages that must be found, use server rendering or static generation, through Next.js, React Router's framework mode or pre-rendering.
• Make sure each route has its own title and description in the served HTML.
• Use real links with href attributes, not click handlers, for navigation.

Check what your server sends: view the page source, not the inspector. If the content is not there, many crawlers will not see it either.

Common mistakes

• Ignoring console errors and warnings that point at real bugs.
• Using div with onClick instead of button, which breaks keyboard and screen reader access.
• dangerouslySetInnerHTML with unsanitised content, which opens XSS.
• Large bundles from importing whole libraries for one function.

What a scan can and cannot tell you

WebAuditOS compares the served HTML with the rendered page, so it shows how much of a React site exists only after JavaScript runs, and it checks titles and descriptions in the served HTML. It also records console errors.

It does not review your components or code quality.

A React site can look perfect in the browser and be an empty page to a link preview bot. The served-versus-rendered comparison shows the gap.

Short answers

Is React a framework? It is a library. Next.js is a framework built on React.

Is React good for SEO? It can be, with server rendering or pre-rendering.

Is React free? Yes, it is open source under the MIT licence.

Should I learn React or Next.js first? Learn React's basics, then a framework for real projects.