Frequently asked questions
Everything you need to know about Core Web Vitals monitoring, real user data, and how Joltsite works.
Core Web Vitals
- What are Core Web Vitals?
- Core Web Vitals are a set of metrics defined by Google that measure real-world user experience on web pages. They focus on three aspects: loading speed (LCP), visual stability (CLS), and responsiveness (INP). Google uses these metrics as ranking signals in search results, making them important for both user experience and SEO.
- What is LCP (Largest Contentful Paint)?
- LCP measures how long it takes for the largest visible element on the page (usually a hero image, heading, or video) to finish rendering. A good LCP is under 2.5 seconds. A slow LCP often means images aren't optimized, render-blocking scripts are delaying paint, or the server is responding too slowly.
- What is CLS (Cumulative Layout Shift)?
- CLS measures how much the page layout shifts unexpectedly while loading. When an ad loads late and pushes content down, or a font swap changes text size, that's layout shift. A good CLS score is under 0.1. Joltsite identifies the exact DOM element causing each shift so you can fix it directly.
- What is INP (Interaction to Next Paint)?
- INP measures how quickly your page responds to user interactions: clicks, taps, and key presses. It captures the time from when a user interacts to when the browser paints the visual result. A good INP is under 200ms. Long-running JavaScript is usually the culprit.
- What are FCP and TTFB?
- FCP (First Contentful Paint) measures when the first piece of content appears on screen: any text, image, or SVG. TTFB (Time to First Byte) measures how long the browser waits before receiving the first byte of the response from the server. They're not Core Web Vitals, but they're key diagnostic metrics that often explain a slow LCP.
- What are "good" Core Web Vitals scores?
- Google defines three ratings for each metric. For LCP: good is under 2.5s, needs improvement is 2.5–4s, poor is over 4s. For CLS: good is under 0.1, needs improvement is 0.1–0.25, poor is over 0.25. For INP: good is under 200ms, needs improvement is 200–500ms, poor is over 500ms. Scores are measured at the 75th percentile, meaning 75% of your visitors need to have a good experience for the metric to pass.
Real User Monitoring
- What is Real User Monitoring (RUM)?
- RUM collects performance data from actual visitors using your site in the real world. Unlike lab tools like Lighthouse that test from a single location on a simulated device, RUM captures data from every real page load, on real devices, real networks, and real browsers. This means you see how your site actually performs for your audience, not in a controlled test.
- How is RUM different from synthetic testing?
- Synthetic tools (Lighthouse, PageSpeed Insights, WebPageTest) run tests from a controlled environment. They're useful for catching issues in development, but they don't reflect real user experience. Your visitors are on different devices, different network speeds, in different countries. RUM captures all of that. A site can score 100 on Lighthouse and still have terrible real-world performance if most users are on 3G mobile.
- What is CrUX data and why isn't it enough?
- CrUX (Chrome User Experience Report) is Google's public dataset of real user metrics collected from Chrome users who've opted in. It's what powers PageSpeed Insights field data. But CrUX only works if your site has enough traffic: roughly 60% of websites don't qualify. And even when you have CrUX data, it's origin-level (not per-page) and updated monthly, with no element-level debugging. Joltsite gives you per-page, per-element data in real time.
- Why does Joltsite use RUM?
- Because real user data is the only source of truth. Lab tests tell you what could happen; RUM tells you what is happening. Joltsite's RUM snippet is under 2KB gzipped, collects no personal data, and gives you element-level debug information that synthetic tools can't provide, like which specific image is your LCP target on mobile, or which DOM element triggered a layout shift.
Pageviews & billing
- What counts as a pageview?
- A pageview is counted each time a visitor loads a page on your site and the RUM snippet sends performance data. One visitor viewing three pages generates three pageviews.
- Do bot visits count as pageviews?
- No. The RUM snippet runs in the browser's Performance API and only fires on real page loads by real browsers. Bots, crawlers, and prefetch requests don't execute JavaScript the same way and are not counted.
- What happens if I exceed my pageview limit?
- Data collection pauses when you hit your plan's limit. You'll see a notification in the dashboard. You can add extra pageview capacity at €30 per million pageviews per month (excl. VAT), or upgrade your plan to resume. We never delete data you've already collected.
- What payment methods do you accept?
- We accept Visa, Mastercard, and American Express credit and debit cards. For European customers, we also support iDEAL/Wero and Klarna. All payments are processed securely through Stripe. You can manage your payment method at any time from your account settings.
Getting started
- How do I set up Joltsite?
- Sign up, add your website, and copy a small JavaScript snippet into your site's HTML — it takes about 2 minutes. You'll see your first data within minutes of your first visitor.
- Does the RUM script slow down my site?
- No. The script is under 2KB gzipped and loads asynchronously after your page content. It uses the browser's built-in Performance Observer API: it observes metrics that the browser already collects, rather than adding its own measurements. There is zero impact on page load time or interactivity.
- Is Joltsite GDPR compliant?
- Yes. Joltsite collects no personal data, sets no cookies, and stores no IP addresses. The RUM snippet only collects performance metrics (load times, element selectors, resource sizes), nothing that could identify a visitor. All infrastructure is EU-based. No consent banner required.
Your next deploy could fix your worst metric
Most performance work stalls because teams can't pinpoint the cause. Joltsite shows you the exact script, element, or page to fix, so your next deploy actually moves the needle.
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