Auto-tagging is a Google Ads setting that adds a unique click identifier to the end of your landing page URL every time someone clicks an ad. That identifier, usually the GCLID, lets Google Ads and Google Analytics match a later enquiry or sale back to the campaign, ad group and keyword that produced it.
How auto-tagging works
With auto-tagging switched on, a visitor who clicks your ad lands on a URL such as yoursite.co.uk/quote/?gclid= followed by a long code. On some Apple devices you may see wbraid or gbraid instead, which carry less detail for privacy reasons. Your Google tag reads the identifier and, through the conversion linker, stores it in a first-party advertising cookie on your domain.
When that visitor later completes a conversion, such as submitting a form, the tag sends the stored click ID back to Google Ads with the conversion. Google looks up the click and credits the right campaign. If your Google Ads account is linked to GA4, the same identifier lets Analytics show Google Ads campaigns, keywords and costs in its reports without you adding any tracking parameters by hand.
Auto-tagging is on by default in new accounts. You can check it in the account settings, and it applies to every campaign in the account at once.
Why it matters
Without a working click ID, Google Ads conversion tracking loses most of its detail, Smart Bidding has less to learn from, and GA4 lumps paid clicks into vaguer categories. You end up paying for traffic you cannot properly judge.
In the UK there is a consent question too. The cookie that stores the click ID is a non-essential advertising cookie, so under PECR it should only be set after the visitor agrees. If your banner is working properly, people who decline will not have the cookie stored. Consent mode handles this by adjusting what Google’s tags do based on the visitor’s choice, and its URL passthrough option can carry the click ID through page URLs instead of a cookie for visitors who have not consented. Expect some gap between clicks and attributable conversions as a result, and plan reporting around it rather than switching off the banner.
Common mistakes
- Redirects or website settings that strip query strings, so the GCLID never reaches the page that holds the tag.
- Forms or booking tools hosted on another domain, where the cookie set on your main site cannot be read.
- Adding manual UTM tags on top of auto-tagging and creating conflicting campaign data in GA4.
- Switching auto-tagging off because a developer saw an “ugly” parameter in the address bar.
- Setting advertising cookies before consent, which breaches PECR even though tracking looks complete.
How to act on it
Confirm auto-tagging is on in your account settings. Then test it: open one of your landing pages with ?gclid=test added to the URL and check that the parameter survives any redirect and stays in the address bar. Run the same test on any third-party booking or payment page in your conversion path.
Next, check your cookie banner blocks advertising cookies until consent and that consent mode is reading the visitor’s choice correctly. If conversions in Google Ads look far lower than enquiries in your inbox, the gap often sits in one of these steps. I check auto-tagging, consent and conversion tracking together as part of Google Ads management.