- Definition
- A click identifier is a parameter such as gclid that an ad platform adds to a landing page URL to connect a visit with the ad click.
In plain words
When someone clicks an ad, the platform can add a unique code to the landing page address. That click identifier lets the advertiser's analytics connect the visit, and any later purchase, back to the click.
On Google it is called gclid. Microsoft Advertising uses msclkid. Both are added automatically when auto-tagging is on, without the advertiser writing them into the ad.
Why it matters for brand and paid search teams
For monitoring, identifiers explain why two captured URLs for the same ad can look different, and why a destination may carry no UTM tags at all.
They also sit next to affiliate and UTM parameters in the same URL. Keeping them apart stops you from mistaking a platform's identifier for a partner code, which keeps affiliate reviews accurate.
How it works
Google explains that auto-tagging adds a parameter called GCLID, short for Google Click Identifier, to the URLs people click through, for example turning a landing page into a URL ending in ?gclid=123xyz. It is needed to track conversions across browsers and to share data with Google Analytics.
The identifier describes one click. It does not identify a person by itself.
Microsoft Advertising's auto-tagging appends a Microsoft Click ID, msclkid, to the landing page URL. Microsoft says it is enabled by default and that the ID is unique for each click, so repeated clicks on the same ad produce different IDs.
Because identifiers are added at click time, a URL captured by monitoring may or may not contain one, depending on how the destination was recorded and whether the advertiser uses auto-tagging.
Example
Northstar's own ad destination, as captured, is northstar.example/boots?utm_campaign=brand_us&gclid=EAIa-sample. A partner's ad destination is northstar.example/boots?aff_id=2231, with no click identifier.
The identifier on Northstar's ad is the platform's measurement. The affiliate parameter on the partner's ad is what links it to the program.
Fictional brands and domains, for illustration only.
Common mistakes and misconceptions
A click identifier identifies the searcher. It links a visit to an ad click for measurement. It is not a name or an account.
The same ad always has the same identifier. Identifiers are generated per click, so they differ between captures.
Identifiers are affiliate IDs. They come from the ad platform. Affiliate IDs come from the program or network.
How to monitor it in Ads Lighthouse
When a destination URL contains click identifiers, the ad details view lists them separately from UTM values and other parameters, so they are never confused with affiliate IDs.
Affiliate ID matching reads only the parameter you configure for your program, so a gclid or msclkid value is never reported as a partner.
Frequently asked questions
What is gclid?
The Google Click Identifier that auto-tagging adds to the landing page URL so a visit can be tied to an ad click.
Should I worry about identifiers in saved URLs?
They are normal measurement parameters. Keep them with the URL as captured. They help explain how the destination was tagged.
What is msclkid?
The Microsoft Click ID that Microsoft Advertising's auto-tagging adds to landing page URLs, so conversions can be tracked back to the ad click.
Official sources
- Google Ads Help: About auto-tagging
- Google Analytics Help: Traffic-source dimensions, manual tagging, and auto-tagging
- Microsoft Advertising Help: Auto-tagging of Microsoft Click ID
Sources checked on .