What detecting Clerk tells you about a site
Clerk is a developer-first authentication and user-management service, and its fingerprint is distinctive: a script from a clerk.* / *.clerk.accounts.dev host, a __clerk-prefixed cookie or session token, and pre-built UI components mounting into the page. Catching it is a strong stack signal — Clerk is heavily adopted by the modern React/Next.js crowd, so its presence usually means a fairly new app built on the contemporary edge-rendered JS stack, by a team that prioritised drop-in auth UI and developer ergonomics over rolling their own.
Clerk in a real-world stack
When you find Clerk, it rarely travels alone. Almost always alongside Next.js or another React meta-framework, frequently with a serverless/edge backend and a hosted Postgres like Neon or Supabase.
About
Clerk is a user management platform.
Categories: Authentication
Quick facts
Detection methodology for Authentication
Auth providers expose a script SDK and (usually) a hosted login endpoint. Auth0's `@auth0/auth0-spa-js` plus `*.auth0.com` redirects; Clerk's `@clerk/clerk-js` plus `clerk.<account>.lcl.dev`; NextAuth's `next-auth` package plus the `/api/auth/...` route handler. We catch each via the bundle and the network requests, plus the exact SDK version from the sourcemap.
How we detect Clerk
Sourcemap Explorer carries 3 fingerprint signals for Clerk, spread across 1 channel — javascript global. The exact patterns are listed below, and you can replay each one in Chrome DevTools to confirm a match by hand.
Each signal alone is rarely conclusive — Sourcemap Explorer cross-references all of them and weights by confidence. You can reproduce any of these checks yourself in Chrome DevTools.
Window-level global the technology installs on page. Reproducible by typing the path into the DevTools console.
window.Clerk.authenticateWithMetamask
window.Clerk.openSignIn
window.Clerk.version = ([\d\.]+)
FAQ
How do I check if a website is using Clerk?
Open the page in Chrome, click the Sourcemap Explorer toolbar icon, and read the Stack tab. Clerk's specific fingerprints here are javascript global, and the popup flags Clerk whenever any combination of them is found. The same checks can be reproduced manually in DevTools — see the "How we detect" section above.
What Clerk version can Sourcemap Explorer detect?
Clerk ships as a hosted authentication rather than a bundled npm package, so version-specific detection isn't always possible. Where the platform leaks a version in response headers (`X-Powered-By`, `Server`, generator meta tags) we surface it; otherwise we report presence only.
Is Clerk a SaaS or self-hosted?
Clerk is offered as a hosted SaaS product. Detection runs against the JavaScript SDK or asset-URL fingerprints the platform ships into pages.
How much does Clerk cost?
Clerk's pricing model is documented as: mid, recurring. Detection is independent of the pricing tier — Sourcemap Explorer flags the technology by its fingerprints, regardless of which paid plan a site is on. See the official site for the current pricing page.
Where can I read more about Clerk?
Official site: https://clerk.dev. For Sourcemap Explorer's detection guide, see the deep-dive link below or the related guides in the cross-link section.
Keep reading on Sourcemap Explorer
Practical guides
Detected by Sourcemap Explorer
Open the popup on any page running Clerkand you'll see the exact version pulled from the bundled package.json when sourcemaps are exposed.