What is the _gcl_au cookie?
This cookie is set by Google Ads and the Google tag/Conversion Linker to store ad-click information on the advertiser's own domain so that subsequent conversions can be attributed to those ad interactions.
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About _gcl_au
| Vendor | |
|---|---|
| Category Category The functional category of the technology, such as Web Analytics or Social Media. Learn more | Advertising & Paid Media |
| Consent Category Consent Category The consent category this cookie most commonly falls under across sites we scan, normalized into four standard categories. Learn more | Targeting & Advertising |
| Prevalence | Very Common |
| Popularity Popularity Popularity is calculated from our dataset of 4.5B+ cookies analyzed across hundreds of millions of web pages. Learn more | Found on 41.6% of scanned pages |
| Expiration Type | Timestamp |
| Expiration Duration | 29 days |
| Party Type Party Type Whether the cookie is first-party or third-party. Learn more | 1st-Party |
| Risk Level Risk Level Rates how sensitive the data stored by this cookie is (High, Medium, or Low) based on data classification and distribution. Learn more | Medium |
| Vendor Privacy Policy | https://policies.google.com/privacy |
| Vendor Website | https://about.google/ |
What is the purpose of _gcl_au?
The _gcl_au cookie is a first-party cookie deployed primarily by the Google tag (gtag.js) and Google Tag Manager's Conversion Linker tag in conjunction with Google Ads and Google Marketing Platform products. Its primary function is to store ad-click information (a pseudonymous identifier) directly on the advertiser's domain. When a user arrives at a site after interacting with a Google advertisement, this cookie helps capture and persist that click context as first-party data.
If the user later performs a tracked conversion action - such as submitting a lead form, completing a purchase, or registering for an account - the information associated with _gcl_au is used to link the conversion back to the original ad interaction. This mechanism enables advertisers to measure campaign effectiveness and attribute cross-page or cross-session conversions using first-party storage. The cookie's default lifespan is 90 days, consistent with the observed expiration distribution.
What are the Privacy Risks of _gcl_au?
Risk Level: Medium
This cookie presents a medium privacy risk because it is used for cross-session tracking and advertising attribution. While it generally stores a pseudonymous identifier rather than plaintext Personally Identifiable Information (PII), it enables the tracking of user behavior and conversion events tied to advertising interactions. The associated data supports Google's advertising measurement and optimization for the advertiser, so it falls under regulatory categories for marketing/advertising data even though it is a first-party cookie.
How to Remove _gcl_au from a Website
To stop this cookie from being set, a website administrator must adjust or remove the Google technology that deploys it. If the cookie is deployed via Google Tag Manager, administrators can pause or remove the Conversion Linker tag, or modify its firing triggers so it does not execute. If deployed via the global Google tag (gtag.js), administrators can remove the configuration that loads the tag, or use the tag's cookie configuration parameters to alter its behavior. Because _gcl_au is integral to Google Ads conversion-linking/attribution, it generally cannot be suppressed independently while still running Google Ads conversion tracking - removing the underlying Google Ads / Google tag scripts from the site entirely is the definitive way to prevent the cookie from being set.