How it works
Most tools work through a small script on every page. Each visit records a page view with details such as the referring site, campaign tags, country, device and browser, plus custom events such as sign-ups, button clicks and purchases. Dashboards turn that into visitors, sessions, top pages, traffic sources, conversion rates and funnels, which show how many people get through each step of, say, a checkout.
The main families are Google Analytics 4 (free, detailed and tied to Google Ads), cookieless tools such as Plausible, Fathom and Umami (simple and privacy-first), and product analytics such as PostHog, Mixpanel and Amplitude, which follow individual users through an app. Server logs and a CDN's own statistics count requests without any script at all.
No tool sees everyone. Ad blockers, declined cookie banners and bots all skew the numbers, so two tools rarely agree exactly. Trends over weeks and months say more than any single figure.
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