How to detect React on any website

What is React?

React is a UI library, not a framework — but it's the default UI layer for Next.js, Remix, Gatsby, parts of Astro, React Native, and countless bespoke setups. Its fingerprints overlap with anything that uses it.

React is the most-used library in frontend JavaScript, and that popularity means its traces are both everywhere and deeply variable. A site might use React as the whole frontend (SPA), as the runtime of a meta-framework like Next or Remix, as an island inside an Astro page, as a widget embedded in a WordPress site, as a native wrapper via React Native Web, or as a small interactive component on an otherwise-static page. Detecting React is rarely the question; detecting 'is React the primary UI layer' or 'which React version is this' is what actually matters. Since React 18 the concurrent-rendering features and Server Components have shifted the ecosystem toward hybrid SSR/streaming models, which changes both what you see in the browser (flight payloads, streamed chunks) and what constitutes a confident detection.

Why it matters to identify

Confirming React is the first step before identifying the framework on top (Next, Remix, Gatsby, Astro, bespoke Vite + React, CRA). Version matters because React 18 and 19 enabled concurrent features and server components that older detectors may not surface. Library ecosystem choices correlate strongly with React version — React 19 sites often run Next.js 15, Server Components and the new use() hook, while React 17 sites are still running CRA or legacy SSR stacks.

A brief history of React

React was open-sourced by Facebook in 2013 and has been the dominant JavaScript UI library since around 2016. Major releases: 16 (2017, Fiber reconciliation), 16.8 (2019, hooks), 17 (2020, no new features — stepping stone release), 18 (2022, concurrent rendering), 19 (2024, actions, use() hook, ref-as-prop, form actions, built-in streaming). Each major version shifted what's possible in the ecosystem: hooks redefined component authorship; concurrent rendering redefined the relationship between UI updates and I/O; server components redefined where code runs.

Ecosystem and common pairings

React's immediate ecosystem is enormous. The common companions: a meta-framework (Next, Remix, Gatsby), a state library (Zustand, Redux Toolkit, Jotai), a data-fetching library (TanStack Query, SWR, Apollo Client for GraphQL), a UI kit (shadcn/ui, MUI, Chakra UI, Ant Design), a form library (React Hook Form, Formik, Conform), styling (Tailwind, styled-components, emotion, CSS Modules). The exact combination often fingerprints the team's vintage and taste.

Detection signals we look at

Each signal alone is rarely conclusive; the detector cross-references all of them and weights by confidence. You can reproduce any of these checks yourself in Chrome DevTools.

[data-reactroot]

window.React.version

node_modules/react-dom/|node_modules/react/

react.production.min.js|react-dom.production.min.js

data-react-helmet|data-rh

Versioning

What you typically see in production

On a typical 2025-2026 React site the bundle weighs anywhere from 40 KB (a tightly tree-shaken Preact-compat island) to 400+ KB (a complete dashboard with Recharts, Radix, TanStack Query, react-hook-form and a custom design system). The sourcemap, when exposed, gives the full picture: `node_modules/react/package.json` for the canonical version, `node_modules/react-dom/package.json` for the renderer version (almost always identical), plus `node_modules/scheduler/` for the concurrent-rendering scheduler library that React 18+ ships alongside. You see two distinct deployment shapes in the field. The first is a meta-framework SPA — Next.js or Remix in the lead — where React is bundled deeply and the sourcemap surfaces the entire dependency surface. The second is the island pattern, popularised by Astro, where React appears in localised chunks attached to specific components (`<astro-island>` markers in the DOM, separate hydration scripts, smaller per-island bundles). The island pattern reduces the apparent React footprint dramatically but does not change the per-island detection signals. React 18 and 19 both exist in the wild today. Most production sites are still on 18.2.x or 18.3.x as of mid-2026 (the long tail of `next@14` and the Remix ecosystem); React 19 is concentrated in early-adopter Next.js 15 builds, anything using server actions seriously, and frontier-engineering teams that have moved past the migration tax. Sites that do not look like meta-framework SPAs at all — embedded widgets, WordPress plugin frontends, micro-frontend shells — typically run an older React (16.x, 17.x) because the dependency cost of upgrading is not worth it for a small surface area. A distinctive pattern when you see Server Components in the wild: `self.__next_f.push(...)` calls in inline scripts, RSC flight payload chunks loaded from `/_next/static/chunks/app/`, and a much thinner client bundle than a comparable client-side-rendered React app. The chunk-loading pattern by itself is enough to tell you the site is on App Router with Server Components active, even before you check the version.

Sites commonly running React

• facebook.com
• instagram.com
• airbnb.com
• netflix.com (parts of)
• whatsapp.com
• x.com

Often confused with

FAQ

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