What it does
Google's definition: "Conversion linker tags are used to help tags measure click data so that conversions are measured effectively."
Here is the problem it solves. Someone clicks your ad and lands on your page with ad click details in the URL, like the gclid. Then they move to a form step or a thank-you page, and that URL detail is gone. The conversion linker grabs the click details on the first page and saves them on your own domain, so the conversion tag can find them later.
Google says it saves the data in first-party cookies with names starting with _gcl_, such as _gcl_aw and _gcl_gs, and in browser local storage under _gcl_ls.
When you need it
Google says to put the conversion linker on any page where visitors might land after clicking an ad, and usually recommends the All Pages trigger in Tag Manager.
You do not need it if your Tag Manager container already loads a Google tag, or a matching Destination tag, on every page. Google also says Google Ads containers automatically load a Google tag first when no connected Destination tag exists.
If your lead flow crosses domains, for example a landing page on one domain and a booking page on another, Google's settings include "Enable linking across domains" with a list of domains to link.
If you are not sure whether you need it, the safe default is to have it on every page your ads send people to. Without stored click details, a form fill on the next page can show up in Google Ads without its link to the ad click, or not show up at all.
When it gets turned off
Each Google tag that reads this data has an "Enable Conversion Linking" option, on by default. Google says setting it to false stops that tag from working with conversion linker data. A setting changed during testing can quietly stay that way.
A free ClickMend scan of your ad's final URL checks whether the conversion linker is turned off, whether a Google Ads conversion tag is on the page and actually loaded, and whether the conversion ID is still a placeholder. If conversions stopped showing up, walk through conversion tracking not working next.
Frequently asked questions
Do I need a conversion linker if I use the Google tag?
Google's Tag Manager help says you do not need one if your container already loads a Google tag, or a matching Destination tag, on every page.
What trigger should the conversion linker use?
Google says it usually recommends the All Pages trigger, so the tag is on any page people might land on after an ad click.
Can ClickMend tell if the conversion linker is off?
Yes. The ClickMend scan checks whether the conversion linker is turned off on the page your Google Ad sends people to.