React: Frontend library detection

What React is

React is a browser rendering library rather than a server framework, so it leaves traces in the delivered markup rather than in response headers. Modern builds are also deliberately quieter than older ones, which makes React one of the harder technologies to confirm from the outside.

How DNSTrace.dev detects it

Detection reads the final HTTPS response and the first bytes of its markup. One matching signal is reported as strong evidence; two or more independent signals are reported as confirmed.

data-reactroot in markup — The hydration root attribute emitted by older server-rendered React output.
__reactContainer$ in markup — An internal container key that appears in some client-rendered builds.

What a detection proves

React rendered part of the delivered page.

What it does not prove

The React version, or the framework around it. Current React versions removed the data-reactroot attribute, so a React application can show no signal at all, and absence is not evidence that React is unused.

Common questions

Why is React often not detected?

React 18 and later no longer emit data-reactroot, and bundled code hides the library name. DNSTrace.dev reports what is publicly visible rather than inferring React from a framework.

Does Next.js imply React?

Next.js is a React framework, but DNSTrace.dev keeps the two detections independent and only reports React when React's own markers are present.