Client-Side Tracking

Client-side tracking is the classic form of tracking: a JavaScript snippet or tracking pixel runs in the visitor's browser (the client), captures page views, clicks or form submissions and sends that data straight from the browser to Google Analytics, Meta, TikTok and others.

How client-side tracking works

Each platform gets its own script on the website – usually via a tag manager. When a visitor loads the page, their browser loads these scripts, sets cookies and sends a request to each platform for every event. The platform links the event to the ad click via cookies and click IDs.

Limits of client-side tracking

• Ad blockers: Many blockers suppress known tracking domains entirely.
• Browser protections: Safari (ITP) and Firefox limit cookies, and third-party cookies are increasingly blocked.
• Consent: If a visitor declines in the banner, many scripts aren't allowed to load at all.
• Browser events only: What happens after the visit – a phone call, a meeting, a deal closed in the CRM – is never seen by a browser script.
• Performance: Five pixels mean five extra scripts slowing down your page.

Example

A coaching business gets 200 leads a month through its form. The Meta Pixel reports 150 of them. The other 50 are still real leads – they just weren't captured because the pixel was blocked or there was no consent. Meta is optimizing on 75% of the data.

Client-side vs. server-side tracking

With server-side tracking, events are sent to the platforms from a server instead of the browser, for example through a Conversion API. In practice, good setups combine both: a script in the browser captures the session, traffic source and form leads, and the transfer to ad platforms also runs server side.

That's how LeadMetrics works too: a single script captures sessions, UTM parameters and click IDs (lead tracking), and leads, deals and payments are sent via the Conversion API to Meta, Google Ads, TikTok and LinkedIn. For the full comparison, read client-side vs. server-side tracking.