> For the complete documentation index, see [llms.txt](https://doc.batch.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://doc.batch.com/developer/sdk/web/advanced/manage-domains.md).

# Domains and subdomains management

The Web Push standard ties each opt-in to the subdomain on which it was collected: users who opt in to push notifications on `domain.com` are not automatically opted in on `shop.domain.com`. This page explains why, and describes three architectures you can choose from depending on whether your subdomains share a single userbase and purpose or not.

## Why is opt-in bound to a single subdomain?

With Web Push, the push token and the notification permission are bound to the exact subdomain where they were collected. The browser treats each subdomain as a separate installation, with its own opt-in request. As a result, an opt-in on one subdomain does not carry over to another.

This is a constraint of the Web Push standard itself, not a Batch limitation, so it applies regardless of how you configure your project. The standard does not allow cross-domain or cross-subdomain subscriptions. Two consequences follow from it:

* A separate opt-in request appears on each subdomain where you deploy the Batch SDK.
* If users accept the opt-in on two subdomains linked to the same project, a full-base campaign reaches these users twice.

The recommended architecture depends on whether your subdomains belong to the same product and audience, or to distinct ones.

## Case 1: Subdomains of the same product, shared userbase and purpose

This is the most common case. Examples include country sites served on several domains (`domain.fr`, `domain.it`, `us.domain.com`) or several sections of the same product.

Recommended architecture:

* A single project on the Batch dashboard.
* One main subdomain referenced on the project, for example, the one with the most traffic.
* The other subdomains added under **Settings > Channels > Push > Push Configuration: Web >** [**Allowed Origins**](https://doc.batch.com/developer/sdk/web/testing-integration#allowed-origins).
* The Service Worker (`batchsdk-worker-loader.js`) hosted at the root of each subdomain.
* The same JavaScript tag on every subdomain.

For targeting:

* To target the users of one specific subdomain, plan a dedicated custom attribute in your tagging plan, for example `domain_visited = "fr"`.
* An opt-in request appears on each subdomain. If users accept the request on two subdomains and you send a full-base campaign, these users receive the push twice.

## Case 2: Subdomains with distinct userbases and purposes

Examples include a corporate site alongside an e-commerce site, two sister brands on separate subdomains, or two independent products.

Recommended architecture:

* One project per subdomain, each with its own userbase.
* The Service Worker hosted on each subdomain.
* A different JavaScript tag on each subdomain.

With this setup, a separate opt-in request appears on each subdomain, and you target users of a given subdomain through their own project.

## Case 3: One main domain, opt-in collected on a single subdomain, deeplinks to the others

Use this when you want to collect push opt-ins only on one subdomain, for example the home page, while still routing notification clicks to a secondary store subdomain.

Recommended architecture:

* A single project linked to a single subdomain.
* The Service Worker and the JavaScript tag deployed only on the subdomain where opt-in is collected and data is reported.

Deeplinks inside the notifications can still send users to any subdomain. Opt-in collection and click destination are independent.

## Related resources

{% hint style="info" %}

* [Web SDK prerequisites](https://doc.batch.com/developer/sdk/web/getting-started/prerequisites)
* [Custom User ID](https://doc.batch.com/developer/sdk/web/profile-data/custom-user-id)
  {% endhint %}


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