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

# What is first-party attribution?

> Understand first-party attribution, what first-party signals SourceMedium uses, and how it relates to last-click and MTA

**First-party attribution** uses data you collect and control from your own properties (your site/app and checkout) to understand which marketing touchpoints contributed to purchases.

In practice, this typically includes **First-Party Inputs** from multiple sources:

* **Website Events**: pixel-based tracking (e.g., GA4, Elevar)
* **Server-Side Capture**: API-based tracking (e.g., Shopify Order Attributes, Connectors)
* **Landing Page Data**: Referrer and URL parameters captured at the start of the session

SourceMedium aggregates all these *First-Party Inputs* to build a complete picture.

## First-party vs platform-reported attribution

* **First-party**: derived from your site/app + checkout signals (what happened on your properties)
* **Platform-reported**: derived from ad platforms (what platforms believe happened based on their measurement and models)

Both can be useful; they often differ due to attribution windows, privacy restrictions, and identity resolution.

## What counts as a first-party signal in SourceMedium

Common examples include:

* Website analytics/event streams (e.g., GA4, Elevar)
* Landing page + referrer capture (including UTMs when present)
* Checkout/order-level capture for UTMs (useful when browser tracking drops parameters)

## Where first-party attribution shows up in SourceMedium

* **Last-click attribution (UTM-based)**: relies on UTMs/landing/referrer capture to assign the most recent touchpoint.
* **Multi-touch attribution (MTA)**: uses first-party purchase journeys (touchpoints) to model first touch, last touch, and linear attribution across the journey.

## Common failure modes (and how to reduce them)

* **`(direct) / (none)` growth**: usually missing UTMs or UTMs being dropped during the journey (cross-domain/checkout).
* **Cross-domain/checkout breaks**: customers move between domains or checkout flows and attribution context is lost.
* **Browser/privacy restrictions**: ad blockers, iOS privacy features, and browser changes reduce client-side tracking reliability.

<Tip>
  Start with consistent UTM setup, then ensure you are capturing data across both client-side (pixel) and server-side (API) inputs to maximize coverage.
</Tip>

## External resources

* [Shopify Checkout UI Extensions](https://shopify.dev/docs/api/checkout-ui-extensions) — For building server-side UTM capture (Shopify Plus)

## Related resources

<CardGroup cols={2}>
  <Card title="UTM Setup" icon="bullseye" href="/help-center/core-concepts/attribution/utm-setup">
    What UTMs are and how to implement them across channels.
  </Card>

  <Card title="Attribution Health" icon="heart-pulse" href="/data-inputs/attribution-health/index">
    Find and fix tracking gaps that reduce first-party coverage.
  </Card>

  <Card title="MTA Overview" icon="sitemap" href="/mta/mta-overview">
    How SourceMedium builds multi-touch attribution from first-party purchase journeys.
  </Card>

  <Card title="GA4 Common Failures" icon="info" href="/data-inputs/platform-supporting-resources/ga4/google-analytics-common-failures">
    Troubleshoot common analytics issues that impact event-based attribution.
  </Card>

  <Card title="Backfilling UTM Attribution via Order Attributes" icon="code" href="/data-inputs/platform-supporting-resources/shopify/backfilling-utm-attribution-via-checkout-attributes">
    Shopify Plus developer guide for capturing UTMs at checkout.
  </Card>
</CardGroup>