# Identity Resolution

> Understand how AnyTrack identity resolution links sessions across devices, domains, and time so conversions stay attributed to the campaign that started the journey.

A visitor clicks your ad, lands on your site, and leaves. Three days later they come back on their phone, type your address directly, and buy. How does that purchase still get credited to the ad that started it? That job is called identity resolution, and AnyTrack does it automatically. You do not configure it or turn it on.

The short answer: AnyTrack collects a set of durable signals the moment a visitor arrives, stores them as first-party data, and then matches every later session and conversion back to the same visitor profile, even when the original UTM parameters are long gone from the URL.

## What identity resolution is

Identity resolution is the process of matching incoming sessions and conversions to the correct visitor profile. It answers a single question: are these two interactions the same person, and which campaign first brought them in?

UTM parameters only appear on the URL at one moment, the landing from a campaign. They then drop out of the address bar as the visitor browses, and they are usually absent entirely when that person returns directly, from email, or on another device. Without a way to reconnect those visits, every return would look like brand-new, unattributed traffic. Identity resolution is what stitches them together.

<Callout icon="📘" theme="info">
**The values are already saved**

AnyTrack reads the UTM parameters on the first page load and stores them as first-party data on the session. After that the URL can change freely. Attribution never depends on the UTMs staying in the address bar.
</Callout>

## How AnyTrack resolves identity

AnyTrack does not rely on one identifier. It resolves identity server-side and from browser signals, combining several layers so that a match survives cleared parameters, new sessions, and device switches. The main signals are:

- **The AnyTrack first-party cookie (`_atcid`)** — set on your own domain with a two-year lifetime. It recognizes the same browser across sessions over time, and the companion `_atutm` cookie remembers the campaign parameters the visitor first arrived with. See [First-Party Data](/docs/first-party-data).
- **The AnyTrack Click ID (`click_id`)** — ties an outbound click to the conversion it eventually produces, even when that conversion happens on a different domain. This is also what [AutoTag](/docs/autotag) carries across domains and what affiliate postbacks match on.
- **Ad platform cookies** — signals like `_fbp` (Meta) and `_ga` (Google) connect a conversion back to the ad click that opened the session.
- **Hashed customer data** — when an email, phone, or name is collected through a webhook, CRM, or form, AnyTrack uses it to link a returning visitor to their earlier interactions, including across devices. This data is hashed with SHA-256 before it is ever sent to an ad platform.

Together these signals let AnyTrack carry the first campaign touch forward through the whole journey. The [data orchestration walkthrough](/docs/anytrack-data-collection-capabilities-and-scopes) shows the same matching happening step by step across a real click-to-conversion path.

## Why attribution survives UTMs leaving the URL

This is the design decision that surprises people. AnyTrack tracks every session and every conversion whether or not UTM parameters are present. Tracking does not require them.

What UTMs do is supply the campaign label. Identity resolution preserves that label by attaching it to the visitor profile on the first visit, then reattaching the profile to each later session. So a conversion that happens days later, on a UTM-free direct visit, still rolls up to the campaign that earned the first click.

The one thing identity resolution cannot invent is a campaign that was never recorded. If no visit in the journey ever carried a UTM, AnyTrack still tracks the session and the conversion, but there is no source to attribute it to in your reports. That is why campaign URLs need UTM parameters even though the rest of the journey does not. See [UTM Parameters](/docs/utm-parameters) for how those values are structured.

## What identity resolution can and cannot do

Identity resolution is strongest when it has durable, first-party signals to work with. It is not magic, and a few real-world limits apply:

- **Cross-session, same browser** is the most reliable case. The `_atcid` cookie holds for two years unless the visitor clears it.
- **Cross-domain** works because the `click_id` travels with the visitor between your site and a merchant or affiliate domain.
- **Cross-device** depends on a shared identifier. AnyTrack can link two devices when the same person provides a matchable signal on both, such as the same email at checkout. With only anonymous browsing on a second device, there is nothing to match on.
- **Privacy controls matter.** Cleared cookies, private browsing, and aggressive blockers reduce the signals available, which is one reason server-side collection is valuable. See [Server-Side Tracking](/docs/server-side-tracking).

## How identity resolution shapes your results

Identity resolution feeds two outcomes you can see in the product:

| Outcome | What identity resolution contributes |
|---------|--------------------------------------|
| Attribution reports | Keeps the first campaign touch attached to later sessions, so the [Campaign Report](/docs/campaign-report) credits the right source even after UTMs disappear. |
| Ad platform match rates | More matched signals raise [Event Match Quality](/docs/facebook-event-match-quality) on Meta and equivalent match rates elsewhere, so platforms attribute and optimize on more of your conversions. |

To protect the first-touch campaign data that identity resolution relies on, configure [Ignored Sources](/docs/ignored-sources) so intermediaries such as PayPal or Mailchimp do not overwrite your stored UTM values mid-journey.

<FaqAccordion
  title="Identity Resolution FAQ"
  icon="fa-duotone fa-circle-question"
  items={[
    {
      question: "Do I need to set up identity resolution?",
      answer: "No. Identity resolution runs automatically once the AnyTrack Tracking Tag is installed and your integrations are connected. There is no switch to enable and no configuration to manage. AnyTrack collects the signals it needs on every visit and matches them behind the scenes."
    },
    {
      question: "How does AnyTrack attribute a conversion after the UTM parameters are gone?",
      answer: "AnyTrack stores the UTM values as first-party data on the first page load. From then on it identifies the visitor through the <code>_atcid</code> cookie, the AnyTrack <code>click_id</code>, ad platform cookies, and hashed customer data. The original campaign stays attached to that profile, so a later UTM-free visit still credits the right campaign."
    },
    {
      question: "Can AnyTrack track a visitor across devices?",
      answer: "Across devices, AnyTrack needs a shared signal to match on, most commonly the same email collected at checkout or in a form. When that signal exists on both devices, the sessions are linked. A second device with only anonymous browsing has nothing to match against, so it cannot be connected."
    },
    {
      question: "Why do some events show the customer's name and email while others don't?",
      answer: "An event carries customer data when the visitor provides it at that moment (for example, AddPaymentInfo or Purchase) — or when AnyTrack already knows who the visitor is. For a first-time visitor, earlier events like InitiateCheckout have no identity to show yet. Once the customer has been identified, AnyTrack resolves their identity as soon as they return to your site, and all their events carry the customer's identity — including event types that don't collect customer data themselves. You can see this in the <a href='/docs/conversions-report'>Conversions Report</a> event details."
    },
    {
      question: "Does AnyTrack track sessions that have no UTM parameters?",
      answer: "Yes. Every session and conversion is tracked whether or not UTMs are present. UTMs only supply the campaign label. If no visit in the journey ever carried a UTM, the conversion is still recorded but has no campaign source to attribute it to in your reports."
    },
    {
      question: "How does identity resolution affect Event Match Quality?",
      answer: "Stronger identity resolution means more matched signals, such as a hashed email tied to a click. That raises <a href='/docs/facebook-event-match-quality'>Event Match Quality</a> on Meta and equivalent match rates on Google and TikTok, which lets the platforms attribute more conversions and optimize delivery more accurately."
    }
  ]}
/>

## If you want to go deeper

<Cards columns={2}>
  <Card title="Attribution Explained" href="/docs/anytrack-attribution-explained">
    How AnyTrack credits conversions across every channel.
  </Card>
  <Card title="Data Collection and Scopes" href="/docs/anytrack-data-collection-capabilities-and-scopes">
    The six data types and the matching signals behind them.
  </Card>
  <Card title="First-Party Data" href="/docs/first-party-data">
    The cookies AnyTrack sets on your domain and what they store.
  </Card>
  <Card title="Server-Side Tracking" href="/docs/server-side-tracking">
    Why server-side collection strengthens matching and recovery.
  </Card>
</Cards>