_gcl_au — Google Ads / Google Tag
By the OpenCookies team · published 2026-10-22 · updated 2026-10-22
- Service
- Google Ads / Google Tag
- Category
- Advertising and profiling
- Default duration
- 90 days
- Type
- First-party cookie (set by your own site)
- Consent required?
- Yes, before any storage or reading.
What is it for?
Used to measure ad conversions: it links a click on a Google ad to an action on your site.
What does it look like?
The value looks like 1.1.123456789.1700000000: a conversion ID and the creation date.
How to see it in your browser
Open your site, press F12, then choose the “Application” tab (Chrome, Edge) or “Storage” (Firefox). Under “Cookies”, select your site’s address: the _gcl_au cookie appears in the list if present, with its value and expiry date.
What does the rule say?
Targeted advertising, remarketing and profiling require prior, free and informed consent. These cookies cannot be exempted.
How to prevent it before the choice
Set the ad_storage and ad_user_data signals to denied by default in Google Consent Mode, and load the Google Ads tag only after consent.
How OpenCookies handles it
Common services like this one are in OpenCookies’ tracker list: the banner neutralizes their script before the visitor chooses and only restarts it after “Accept”. The test shows whether this cookie appears before the choice, after “Refuse” and after “Accept”.
Step-by-step guide : Google Consent Mode v2: how to set it up simply
Check it on my site
Does this cookie appear on your site before the visitor chooses? The OpenCookies test shows it in two minutes.
Related cookies
Frequently asked questions
What is the “Conversion Linker” for?
It is the Google tag that creates this cookie to link an ad click to an action on your site, even without Google Analytics.
Does consent mode prevent it?
With ad_storage denied, the Google tag does not write this cookie. That is the purpose of Consent Mode.
Durations are defaults and may change with configuration. This page describes a cookie; it is not legal advice.