---
slug: welche-kennungen
title: "Which attributes are linked?"
category: journeys
locale: en
updated: 2026-10-13
keywords: ["identifier","identity","anonymous_id","session_id","click_id","user_id_hash"]
questions: ["How does Metrunio know that two signals belong together?","How are users recognised?","Do you use fingerprinting?","Which IDs do you use?"]
url: https://bench.metrunio.com/en/help/welche-kennungen
---

# Which attributes are linked?

**How does Metrunio know that two signals belong together?**

Only through unambiguous identifiers: session ID, pseudonymous first-party ID, click ID, impression ID, view identifier, pseudonymised customer identifier, and order or lead number. Nothing else.

| Identifier | Origin | Typical use |
| --- | --- | --- |
| anonymous_id | random first-party value in local storage | links visits from the same browser |
| session_id | assigned by the SDK | links events within one visit |
| click_id | from the click tracking URL | links ad click and website |
| impression_id | from the ad server macro | links delivery, viewability and click |
| view_id | metrunio_view cookie of the measurement address, only with marketing consent | links a view to the later visit to the shop (post-view) |
| user_id_hash | tenant-specific pseudonymised customer number | links signed-in visits |
| order_id / lead_id | from shop or CRM | links server-side conversion and website |

## Explicitly excluded

- No fingerprinting through device characteristics.
- No probabilistic models.
- No linking across tenant boundaries.
- No plaintext email addresses or phone numbers; they cause the event to be rejected.

> **Note:** A user_id you pass is pseudonymised on receipt through a tenant-specific HMAC and never stored in clear text. If you already pseudonymise, send user_id_hash directly, for example the SHA-256 of the email address. That value is also combined with your account’s key on receipt: the same checksum yields a different identifier in another account.

For funnel steps a customer identifier is mandatory: a `goal` without user_id, user_id_hash or anonymous_id is rejected, because “once per customer” cannot be decided otherwise. Only with user_id or user_id_hash is the customer the same across browsers and devices; with the anonymous_id alone the step counts per browser.

## Also asked

- How are users recognised?
- Do you use fingerprinting?
- Which IDs do you use?

## Related

- https://bench.metrunio.com/en/help/cross-device
- https://bench.metrunio.com/en/help/server-events-api
- https://bench.metrunio.com/en/help/was-wird-gespeichert
- https://bench.metrunio.com/en/help/funnel-schritte-messen