Inside the 3 kB analytics script

Analytics is supposed to observe your site, not slow it down. Yet the typical tag weighs 45 kB or more, before it fetches anything else. The sonex tracker is roughly 3 kB (2.9 kB brotli, 3.3 kB gzipped). This is what fits in that budget, and why the budget matters.

Why weight matters

Every kilobyte of JavaScript is downloaded over the network, parsed, and executed on the visitor’s device, often a mid-range phone on a slow connection. That work delays interactivity and shows up directly in Core Web Vitals like Interaction to Next Paint. Analytics that hurts the experience it measures is a bad trade.

What fits in 3 kB

The tracker is hand-written vanilla JavaScript with no third-party dependencies. In that space it:

• Loads with defer, so it never blocks parsing or rendering
• Sends a pageview using the browser’s own beacon and keepalive fetch, which survive the page unloading
• Tracks single-page-app navigation through the History API, so route changes count as pageviews
• Reads declarative data-sonex-event attributes for custom events, no extra code required
• Honours Do Not Track and skips visitors who ask not to be counted

What is not in there

The size comes as much from what is absent as what is present. There is no cookie or consent logic, because nothing is stored on the device. There is no fingerprinting library, no identity graph, and no advertising code. Those are the parts that bloat conventional tags, and they are exactly the parts a privacy-first tool does not want.

Declarative by default

Because reading data-* attributes is cheap, most tracking needs no JavaScript at all:

<button data-sonex-event="signup" data-sonex-event-plan="pro">
  Start free
</button>

The attributes ride along as event properties. For anything dynamic, a tiny API is available:

window.sonex.track("checkout", { value: 49 });

The payoff

Small, dependency-free, and deferred means the tracker is effectively invisible to your visitors and to your performance budget. You measure realtime visitors, pages, referrers, funnels and custom events, and your page still loads like the analytics is not there. That is the intended outcome: fast to insight, and quiet by default.