What is a segment?
A segment is a saved set of filtering rules. When a segment is assigned to an experiment, only visitors who match the rules are eligible for bucketing. Visitors who do not match see the default experience and are not tracked.
Segments let you run targeted experiments — for example, testing a mobile layout only on mobile visitors, or running a campaign-specific landing page test only for visitors arriving from a paid ad.
Creating a segment
Go to Segments → New segment in the sidebar. Give it a descriptive name, then add one or more rules.
Available fields
| Field | What it evaluates |
|---|
device | Visitor’s device type, based on window.innerWidth at script load time |
utmSource | utm_source query parameter in the page URL |
utmMedium | utm_medium query parameter in the page URL |
utmCampaign | utm_campaign query parameter in the page URL |
referrer | document.referrer — the URL of the page the visitor came from |
Device detection
Device is determined by screen width at the moment the script runs:
| Width | Device |
|---|
| Less than 768px | mobile |
| 768px to 1023px | tablet |
| 1024px and above | desktop |
Operators
| Operator | Meaning | Example |
|---|
eq | Exactly equal (case-sensitive) | utmSource eq google |
neq | Does not equal | device neq mobile |
contains | String contains the value | referrer contains facebook.com |
Combining rules
Rules within a segment can be combined with AND or OR logic:
- AND — visitor must match all rules to be eligible
- OR — visitor must match at least one rule to be eligible
You can mix AND and OR within the same segment. For more complex logic, create multiple segments and duplicate experiments.
Segment examples
Mobile only
Only visitors on screens narrower than 768px are included.
Paid Google traffic
utmSource eq google
AND
utmMedium eq cpc
utm_source=google&utm_medium=cpc in the URL).
Social traffic
utmMedium eq social
OR
referrer contains instagram.com
OR
referrer contains facebook.com
Exclude direct traffic
Only visitors who arrived from a referring page (i.e. not direct navigation or a typed URL).
Assigning a segment to an experiment
On the experiment Overview tab, use the Segment dropdown to assign a saved segment. You can change this at any time, even while the experiment is running.
Changing a segment on a running experiment takes effect immediately for new visitors. Existing visitors who were already assigned retain their assignment regardless of whether they still match the segment.
How segment evaluation works
Segments are evaluated client-side in the visitor’s browser, before any bucketing happens. The rules are evaluated on every page load using JavaScript:
// Example: device eq mobile
function matchesSegment(rules) {
var device = window.innerWidth < 768 ? 'mobile' : window.innerWidth < 1024 ? 'tablet' : 'desktop';
var params = new URLSearchParams(location.search);
// ... evaluate each rule ...
}
UTM persistence
UTM parameters are only present in the URL when the visitor first arrives from a link that includes them. If a visitor arrives via ?utm_source=google on the first page, then navigates to a second page, the UTM parameters will no longer be in the URL on the second page.
This means segment evaluation works best on the landing page. If your segment depends on UTM parameters, make sure your experiment applies to the landing page itself (not a page the visitor navigates to afterward).
A future version will persist UTM values in a session cookie so they are available across the full visit.
Limitations
- No server-side fields — country, customer login status, purchase history, and Shopify Markets region are not available for segment rules. All evaluation happens in the browser.
- UTM values are not persisted — UTM parameters must be present in the URL at the time the page loads for the rule to match.
- Case-sensitive matching —
eq and contains are case-sensitive. utmSource eq Google will not match utm_source=google.
