What Is a URL Parameter? Types, How to Add Them, and Measurement Use in GA4

Indispensable for accurately analyzing traffic from ads, SNS, and newsletters is the "URL parameter." The string like "?utm_source=..." attached to the end of a URL is exactly that, but surprisingly few people grasp its types, how to add it, and how to read the data in GA4. This article clearly explains everything from the basics of URL parameters to their types, the correct way to add them, measurement use in GA4, and cautions.

What Is a URL Parameter?

A URL parameter is a variable added to the end of a web page's address (URL). Written in the "key=value" format after "?", it serves to pass additional information to servers and analytics tools. For example, in a URL like the following, the bold part is the parameter.

The first symbol connecting the URL and the parameter is always "?", and the second and subsequent parameters are joined with "&". By using this mechanism to pass source information to an analytics tool, you can accurately distinguish "where the user came from."

The Two Types of URL Parameters

URL parameters are broadly divided into two types based on differences in their roles.

• Active parameter: A parameter that changes the displayed content of the page itself. Used for filtering, sorting, and pagination of search results, the displayed content changes depending on the value.
• Passive parameter: A parameter that, even when added to the URL, does not affect the page's displayed content. Also called a "dummy parameter," it is mainly used for traffic measurement in analytics. The UTM parameters described later fall into this category.

What you use when you want to measure the effect of marketing measures in analytics is the latter, passive parameters—and among them, the "UTM parameter."

The Lead Role in Traffic Measurement: "UTM Parameters"

A UTM parameter is a string added to the end of a URL to classify a visitor's traffic path. UTM stands for "Urchin Tracking Module," a name originally derived from the analytics software of Urchin, the company before its acquisition by Google. By adding it to links in ads, SNS posts, and newsletters, you can accurately track in GA4 which path a visit came from.

UTM parameters are important because without them, the traffic source can be misclassified. For example, even a user who came from a Yahoo! ad may be recognized as "yahoo / organic (organic traffic)" without parameters. With correct settings, it can be distinguished as "traffic from an ad," letting you accurately visualize the effect of each measure.

The Main 5 Types of UTM Parameters

There are mainly the following five UTM parameters. GA4 officially recommends setting the three of source, medium, and campaign in particular.