The Kit tag for the Google Tag Manager server container allows you to integrate your website with Kit by creating, updating and unsubscribing Subscribers via Kit’s Subscribers API.
This server-to-server integration helps improve data accuracy and security by communicating directly with Kit from your server, bypassing client-side tracking limitations. Authentication uses a Kit API Key — no OAuth setup required.
Features
- Create Subscriber — creates a new subscriber, or upserts an existing one by email address, via Kit’s Subscribers API. Kit does not support changing the state of an already existing subscriber, so Subscriber State (default: Active) only applies to new subscribers.
- Update Subscriber — updates an existing subscriber’s name and custom fields. Kit identifies subscribers to update by their numeric ID rather than email, so the tag first looks the subscriber up by email and then updates the matched record.
- Unsubscribe Subscriber — unsubscribes an existing subscriber from all future emails, moving them to the
cancelledstate. The tag looks the subscriber up by email and then unsubscribes the matched record. Kit keeps the subscriber’s record, history and tags. Kit treats this as consent-revoking and effectively permanent, so only re-subscribe someone with their explicit permission.
How to use Kit tag
- Add the Kit tag to the server GTM container from the template gallery.
- Add your Kit API Key — found in your Kit account under Settings → Developer. Learn more about locating your API Key.
- Select the Event Type: Create Subscriber, Update Subscriber or Unsubscribe Subscriber.
- Add the subscriber’s email address. Leave it empty to fall back to the event’s email fields when Automap from Event Data is enabled.
- Optionally, set the Subscriber Lookup Status (Update and Unsubscribe only), First Name and Custom Fields (both not used by Unsubscribe Subscriber), and the Subscriber State (Create Subscriber only).
Automap from Event Data
Enabled by default (Automap from Event Data checkbox). When on, the Email Address field falls back to the first available value below if left empty:
eventData.emaileventData.user_data.emaileventData.user_data.email_address
Disable this checkbox to require the Email Address to be set explicitly on the tag.
Subscriber Lookup Status
Update Subscriber and Unsubscribe Subscriber look the subscriber up by email before acting on them. Subscriber Lookup Status selects which subscriber statuses that lookup searches:
- All (default) — also finds cancelled, bounced, complained and inactive subscribers.
- Active — only finds active subscribers. The tag fails for anyone else.
Custom Fields
Kit identifies Custom Fields by their key, not their label. Find each field’s key by opening a subscriber’s Custom Fields from the Subscribers list in the Kit UI. Unknown keys are ignored by Kit. Each row requires a key and a value, and keys must be unique. Kit accepts up to 140 custom fields per request, and processes requests with more than 10 fields asynchronously.
Additional information
- Subscriber lookup and caching: Update Subscriber and Unsubscribe Subscriber look the subscriber up by email, using the selected Subscriber Lookup Status. A successful lookup is cached in memory on the server, scoped to the API Key, lookup status and email address, and reused by later events handled by the same server instance. A failed lookup is never cached, and the cached entry is dropped if Kit answers
404for it. - API rate limit: Kit limits API Key requests to 120 per rolling 60 seconds. A non-cached Update or Unsubscribe event makes two requests: the lookup and the update.
- Use Optimistic Scenario: calls
gtmOnSuccess()without waiting for Kit’s response. This speeds up the server container response, but reports success even if the API call fails. - Tag Execution Consent Settings: the tag can send data always, or only when marketing consent (
ad_storage) is given. When consent is required and not given, the tag doesn’t send anything and finishes as successful. - GTM preview requests (page location starting with
https://gtm-msr.appspot.com/) are skipped and finish as successful.
Open Source
The Kit tag for GTM Server Side is developed and maintained by Stape Team under the Apache 2.0 license.
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