Measure Core Web Vitals:live, from your first visitor.

Core Web Vitals are the three user-experience metrics Google measures for every website and factors into ranking: LCP (how fast the main content appears), INP (how fast the page reacts to input) and CLS (how much the layout jumps). Google scores them at the 75th percentile; good means LCP ≤ 2.5 s, INP ≤ 200 ms and CLS ≤ 0.1. fastmon measures all three from real visits, plus diagnostics like TTFB, FCP and page load time.

There are two complementary ways. A lab test (Lighthouse, PageSpeed Insights) loads your page on a simulated device: reproducible, but it does not show what your visitors experience. Web vitals monitoring (Real User Monitoring) measures every real load time in your visitors' browsers, on their devices and networks, aggregated at the p75. fastmon makes this field data visible from your first visitor, without 28-day averages, and adds scheduled Lighthouse audits if you want them.

In most cases yes, but for a different reason than with classic analytics tools. fastmon itself sets no cookies* and, in the default (read-only) mode, stores nothing on the device. The IP address is reduced to a country code at the edge and discarded immediately, query strings are stripped, and there are no long-lived or cross-site identifiers. What remains is read access to browser APIs (the Performance API for Web Vitals, viewport, errors). Under the prevailing interpretation this access falls under § 25 (1) TDDDG and requires consent. The website operator obtains that consent through their consent management platform, exactly as with other tools; the responsibility sits with the operator and is described in our privacy policy (section 5.5). The difference from cookie-based trackers shows at opt-out: if a visitor declines, fastmon measures nothing for that visit, exactly as it should. What does not happen, though: no double-counted users, no orphaned sessions, no distorted unique counts, because fastmon never builds a long-lived or cross-site recognition that could break in the first place. fastmon measures aggregate field performance from a sample, and a smaller sample stays meaningful. So your metrics just get smaller, not skewed, whatever your opt-out rate. With cookie-based tools every opt-out additionally costs you recognition, and with it the reliability of your user numbers.

There are solid field studies on this. The Deloitte/Google study 'Milliseconds Make Millions' (2020) measured across 37 brands and over 30 million sessions that a 0.1 s faster mobile load time went along with +8.4% conversion and +9.2% average order value in retail, and +10.1% conversion in travel. Per Google/SOASTA data (2017), the probability of a bounce increases 32% as load time grows from 1 s to 3 s. These are correlations from field studies, not a guarantee for your site: your effect depends on your website, your industry and your implementation. That is why our calculator works transparently with a disclosed model factor and promises you nothing.

fastmon Light starts at €29 a month with 200,000 pageviews: Core Web Vitals, Real User Monitoring, web analytics and alerts. Standard from €99 adds full debugging, synthetic monitoring and fastmon AI. Both hosted in Germany, live in about five minutes, no credit card to start.