> ## Documentation Index
> Fetch the complete documentation index at: https://arkticstudio.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Segments

> Target your experiment to a specific subset of visitors using device, UTM parameters, and referrer rules.

## 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` |

Note that this is viewport width, not physical device type. A tablet in landscape mode may be classified as desktop. A desktop browser window resized to narrow width may be classified as mobile.

### 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

```
device eq mobile
```

Only visitors on screens narrower than 768px are included.

### Paid Google traffic

```
utmSource eq google
AND
utmMedium eq cpc
```

Only visitors arriving from a Google paid ad (with `utm_source=google&utm_medium=cpc` in the URL).

### Social traffic

```
utmMedium eq social
OR
referrer contains instagram.com
OR
referrer contains facebook.com
```

Visitors from any social channel, whether tracked via UTM or referrer.

### Exclude direct traffic

```
referrer neq ""
```

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:

```js theme={null}
// 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 ...
}
```

If a visitor does not match the segment, the entire experiment is skipped — no bucketing, no assignment, no tracking.

### 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).

<Note>
  A future version will persist UTM values in a session cookie so they are available across the full visit.
</Note>

***

## 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`.