UnderTheHood - Check Which Technology Is Behind Any Website

See what any website is built with: detect its full tech stack, 500+ technologies, plus security, SEO & speed checks.

See what any website is built with, in one click. UnderTheHood is a website technology checker that reads the tools running behind any page and turns them into a clear report. Open it on a site and you get its full tech stack, plus a breakdown of the site's security, speed, SEO and hosting. Most "what technology is this website using" tools stop at a list of names. This one keeps going. You get version numbers, confidence levels, a security grade, real Core Web Vitals, DNS records and an on-page SEO audit, in an interface inspired by Notion. WHAT IT DETECTS More than 500 technologies across 70+ categories, each tagged with a confidence score and a version number where the page exposes one. The categories include: • JavaScript frameworks, libraries and meta-frameworks • Content management systems, site builders and headless CMS • Ecommerce platforms and payment processors • UI and CSS frameworks, fonts and icon sets • Hosting, PaaS, CDNs and cloud providers • Analytics, tag managers, advertising and marketing tools • Live chat, search, maps and video players • Security, bot protection, consent and accessibility tools Every result shows the signal that triggered it, so you can trust the match instead of guessing. THE FULL SITE BREAKDOWN • Security: a letter grade for the site's HTTP security headers (HSTS, CSP, X-Frame-Options and more), with plain explanations of what is missing and how to fix it. A cookie audit checks the Secure, HttpOnly and third-party flags. • Speed: real Core Web Vitals measured from the page you are on (LCP, CLS, FCP, TTFB), plus connection timing, HTTP version and page weight by request type. • Network: the resolved IP address, HTTP status and full DNS records (A, AAAA, NS, MX, TXT), so hosting, mail and domain verification are easy to read. • Headers and cookies: every response header in full, and each cookie with its domain and security flags. • SEO: checks for the title, meta description, canonical, viewport, headings, structured data and robots rules, with a Google search preview and an Open Graph social-card preview. EXPORT YOUR RESULTS Copy a tidy Markdown report, or download the whole analysis as JSON or CSV for audits, spreadsheets and prospect lists. WHO USES IT • Developers checking what a client or competitor site runs • Agencies auditing a site before a pitch, redesign or migration • SEO and marketing teams reviewing tags, analytics and on-page setup • Sales teams building lead lists by technology • Anyone curious about what powers the sites they visit MORE THAN A TECHNOLOGY LIST Other detectors stop at naming the tools a site uses. UnderTheHood adds the security-header grade, real Core Web Vitals, DNS records and the on-page SEO audit, so you get the full picture of a site in one place. You do not need an account, and the core features are free. PRIVACY Detection runs on your device. The only network requests are a headers check on the page you are viewing and a DNS lookup through Google's public resolver. Your browsing is never sent to a server, because there is no server. HOW TO USE IT Install the extension, open any http or https site, and click the icon. The report loads in about a second. Switch between light and dark themes in settings. Spotted a technology we missed? Leave a review; we read every one.