What we did

An in-house VANTAG tool to audit any website straight from the browser, without leaving the tab. A single popup with six diagnostic tabs:

Web Vitals — Core Web Vitals (LCP, CLS, INP, FCP, TTFB) in real time, compared against real-user data (CrUX) and with concrete improvement suggestions.
Server Info — IP geolocation, provider (ISP), ASN, time zone and hosting details.
DNS Info — A, AAAA, MX, NS, TXT, SOA and CNAME records, plus subdomain discovery.
SEO — on-page audit with a score, domain authority estimate, structured data and Open Graph.
Tech Stack — automatic detection of CMS, frameworks, analytics, fonts and server technology.
A11y — accessibility audit with an estimated WCAG level and issue detection.

It also exports a full Markdown report in one click, has light/dark mode and works in the Chrome side panel.

It started as support for our optimization work: the analysis runs locally and we don’t send your personal data or browsing history to our servers. Field, IP and DNS data are fetched from public APIs (CrUX, Google DNS, among others).

How we built it

A fork of Google’s official Web Vitals extension, extended by VANTAG and released under the Apache 2.0 licence. Metrics are captured with the web-vitals library on top of the PerformanceObserver API; packaged for Chrome/Edge (Manifest V3, with a service worker).

The popup shows each metric with its threshold (good / needs improvement / poor) and the element responsible for it. For data that isn’t available in the browser it consumes public APIs with no user key: Chrome UX Report (CrUX) for field data, ipwhois for geolocation, Google Public DNS for DNS records, Mozilla HTTP Observatory for security headers, and RDAP for domain registration data.