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What's this site
built with?

Paste any website. Sniff reveals its tech stack, how fast it answers, how well it's secured, and the CO₂ every visit costs.

What is duolingo.com built with?

Duolingo — Duolingo is the world

Tech stack

Scores

Verdict

Duolingo is built with Amazon CloudFront for content delivery, Google Tag Manager for analytics, a PWA architecture, and OneTrust for consent management. Its biggest strength is a solid 87 performance score with efficient resource loading at 687 KB across just 13 requests. The single most critical improvement would be implementing missing security headers—particularly Content-Security-Policy and HSTS—since the site currently carries an F security rating despite all traffic going through third-party services.

Scanned 2026-10-30.

1

Paste any website

Sniff fetches the page once, like a browser would, and weighs every file it loads.

2

See the stack

About 110 fingerprints reveal frameworks, CMSs, hosting, CDNs, analytics, payments and more.

3

Get the scores

Speed, security headers grade and CO₂ per visit, with a plain-English verdict and fixes.

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Questions

How do I find out what a website is built with?

Paste the address into Sniff. It fetches the page once and looks for the fingerprints that frameworks, CMSs, hosting providers, CDNs and analytics tools leave in the HTML, response headers, loaded files and cookies, then lists everything it recognises.

Is Sniff free?

Yes. Sniff is free, needs no sign-up and stores nothing about you. Reports for popular sites are cached for a week so they load instantly.

How is the carbon footprint calculated?

Sniff weighs every file the page loads and applies the Sustainable Web Design model: about 0.81 kWh per gigabyte transferred at the global average grid intensity of 494 g CO2e per kWh, then grades the result from A+ to F.

What does the security grade mean?

It checks six HTTP security headers (HSTS, Content-Security-Policy, X-Frame-Options, X-Content-Type-Options, Referrer-Policy and Permissions-Policy), whether the site uses HTTPS with a valid certificate, and whether it reveals server versions.

Can I compare two websites?

Yes. Choose Compare two, enter both addresses and Sniff shows them head to head on speed, security, carbon, page weight and tech stack, with a winner.

What technologies can Sniff detect?

About 110, including Next.js, React, Vue, Angular, Svelte, WordPress, Shopify, Webflow, Wix, Tailwind, Bootstrap, Cloudflare, Vercel, Netlify, AWS, Google Analytics, Stripe, Razorpay, Intercom and many more.