**Upcoming breaking change (effective July 6, 2026):** Synerise is introducing changes to how user identifiers and UUIDs are handled. These changes may affect profiles with accented or diacritical characters in identifiers, profiles with leading or trailing whitespace in identifiers, and profiles with duplicate UUIDs. For details and recommended actions, see [Upcoming changes to handling identifiers](/docs/settings/configuration/identifier-standardization).
## Anonymous customers When a customer enters your website for the first time, they are anonymous. However, their actions are already being tracked - a UUID is assigned and stored in an anonymous profile in the database. The same UUID is stored in the [cookies](/developers/web/cookies) of the customer's browser. The anonymous profile stores information about the customer's activities, just like it does for recognized customers. The customer can now receive personalized recommendations on the website and be included in marketing campaigns. ## Recognized customers By default, the unique identifier is the customer's `email`. You can [configure your workspace to use `customId` instead](/docs/settings/configuration/non-unique-emails). In the Web SDK and some other contexts (for example, form tracking), `customId` may also be referred to as `custom_identify`. When the customer provides the unique identifier, the anonymous profile in the database is updated with new data. It becomes a known customer profile, which means that any activity before the customer was recognized is still present in the profile's history. A freshly-recognized customer sees personalized content, based on their previous interactions with the website as an anonymous customer. If a recognized customer provides a unique identifier in a form, and another recognized customer's profile already exists in the browser, the context changes to the most recent customer.
It's not necessary for a customer to register an account on your website. A non-anonymous profile may be created based on information provided in other contexts, such as subscribing to a newsletter. See [Tracking form data with SDK](/developers/web/tracking-form-data), [Newsletters](/developers/web/newsletter-agreements), and [Tracking form data with API](/developers/web/tracking-form-data/tracking-form-data-api).
## Recognizing customers from link parameters --- You can append parameters to links to inform the Synerise JS SDK who clicked the link. The parameters are `snrs_cl` (the user's UUID) and `snrs_he` (hash of the user's identifier). A [tracking code](/developers/web/installation-and-configuration) must be implemented in the linked page. The instructions on adding the parameters to the links in templates are available at the links below: - [Email templates](/docs/campaign/e-mail/creating-email-templates#tips-before-you-start) - [Mobile push templates](/docs/campaign/Mobile/creating-mobile-push-templates/mobile-push-visual-builder#adding-tracking-parameters-to-links) - [SMS templates](/docs/campaign/SMS/creating-SMS-template#tracking-parameters-in-links) - [Web push templates](/docs/campaign/Webpush/creating-webpush-templates#tracking-parameters-in-links) When these parameters are present in a link, the user’s browser context is automatically switched to the identified user without any prompt. The primary purpose of this automatic context update is to maintain continuity of the user’s journey after clicking the link—for example, from an email campaign—ensuring that all subsequent [events](/docs/assets/events/introduction-to-events) are accurately attributed to the user whose identifier was included in the link. This mechanism enables seamless user journey continuity but can also lead to context changes when a link is shared with another person. In such cases, the recipient’s browser context will switch to that of the original user, which may affect how events are attributed. On the user interface on the Synerise platform, you can decide how end-user context is managed when these link parameters are detected; the full instruction is available in the ["Managing user context" section](/docs/settings/configuration/non-unique-emails#managing-user-context).