How to tell whether your cookie banner really blocks trackers
By the OpenCookies team · published October 22, 2026
A cookie banner can be perfectly visible and block nothing. What matters is not what the visitor sees, but what the browser sends and stores before they have answered.
The three moments to compare
A serious check looks at three states of the same site:
- Before any choice: the visitor has just arrived and clicked nothing.
- After “Refuse”: they said no.
- After “Accept”: they said yes.
In the first two states, only strictly necessary cookies should remain (for example the one that remembers the choice itself). Audience measurement and advertising cookies should only appear in the third.
Checking by hand
- Open your site in a private browsing window, to start from a clean browser.
- Open the developer tools (F12 key), “Application” tab (Chrome) or “Storage” (Firefox), “Cookies” section.
- Reload the page without touching the banner and note the cookies present.
- In the “Network” tab, check whether requests go out to tracking services:
googletagmanager.com,google-analytics.com,facebook.net,connect.facebook.net,analytics.tiktok.com… - Repeat after “Refuse”, then after “Accept”.
The most common warning signs before any choice: _ga (Google Analytics), _fbp (Meta Pixel) and _gcl_au (Google Ads). Each one has a page in our cookie dictionary.
Why a banner lets trackers through
- The tracking script is hard-coded in the page: it runs before the banner has loaded.
- The banner loads too late (at the bottom of the page, or through a poorly set tag manager).
- A plugin or widget (embedded video, chat, statistics) adds its own script without going through the banner.
- The refusal is recorded, but the tags do not read that choice.
The two-minute check
The manual method takes time and depends on what you know how to spot. The OpenCookies test does these three passes in a real browser, from France or the United States, and shows for each the cookies, the tracking requests and the state of Google Consent Mode. The report only says what is “observed” or “not observed”: it is not legal advice, and it never claims a site is “compliant”.
The test method describes precisely what is measured, and its limits.
What to fix if the test finds a problem
The report ranks findings by priority. In most cases the fix is to load the banner first in the page head and stop tracking scripts from running before consent. Our guides cover the common cases: Google Analytics 4, Consent Mode v2 and WordPress.