GA4 Custom Dimensions: Choose the Right Scope and Register Parameters With AI

Start with the marketing question

A useful custom dimension answers a question that affects a decision.

For a lead-generation website, you might want to distinguish demo requests from newsletter sign-ups. An event parameter such as lead_type can describe the submitted form.

For a subscription product, a user property such as plan_tier can describe the user’s current plan. An ecommerce business might attach item_material to products in its ecommerce events.

Before creating anything, check whether GA4 already provides a suitable standard dimension. Google recommends using predefined dimensions where they already cover the information you need. Google’s custom-dimension setup guidance.

Ask your assistant:

Review these marketing questions and our proposed parameters. Identify which questions can use existing GA4 dimensions. For the remaining questions, recommend a parameter name, scope, example values and the decision the report would support.

Choose event, user or item scope

The place where you send the data should match the scope you register.

A user property needs to be set and updated through your tracking implementation. Registering a user-scoped dimension does not automatically discover someone’s plan.

Item-scoped data belongs inside the relevant item object. Placing the same field at the top level of an event does not give it item scope. Google’s explanation of custom dimensions.

Standard GA4 properties currently allow 50 event-scoped, 25 user-scoped and 10 item-scoped custom dimensions. Use those slots for information you intend to analyse. Google’s custom-definition limits.

Check the dimensions already registered

Connect your property through SourcetoMCP’s Google Analytics connector, then request the existing definitions:

List the custom dimensions on my selected GA4 property. Show each dimension’s ID, display name, parameter name, scope and description. Check whether lead_type already exists with EVENT scope. Report any incomplete-list warnings. Make no changes.

SourcetoMCP’s custom-dimension listing operation returns these configuration fields. It also flags when more definitions exist beyond the returned page.

Check the parameter name and scope together. A similar display name does not establish that two definitions measure the same thing.

Send the parameter before validating the report

Creating a custom dimension registers information for reporting. Your website or app must also send the corresponding data.

For the lead_type example, your tracking implementation could send demo_request when someone requests a demonstration and newsletter when they subscribe.

Your developer or tag manager configuration handles that collection step. SourcetoMCP’s custom-dimension operation changes the GA4 definition. It does not install a website tag or modify Google Tag Manager.

Test the implementation in GA4’s debugging tools and check that the parameter arrives on the intended event.

Use consistent values. demo_request, Demo Request and demo would make the report harder to interpret if they all describe the same action.

Register the approved dimension with AI

After checking the existing definitions and tracking implementation, give your assistant an exact instruction:

On the selected GA4 property, create a custom dimension with display name “Lead type”, parameter name lead_type, scope EVENT and description “Type of lead form submitted”. First confirm that an equivalent definition does not already exist. Create only this approved definition and return its ID and saved settings.

SourcetoMCP supports creating event-, user- and item-scoped custom dimensions. It can also update their display names and descriptions.

Choose carefully before creation. GA4 treats the parameter name and scope as immutable. Correcting either requires a different definition rather than editing those fields. Google Analytics Admin API reference.

Validate fresh data in Analytics

Google advises allowing 24–48 hours after the custom data is sent and the dimension is created before using it in reports and explorations. Google’s reporting guidance.

Build an exploration using the new dimension and the relevant event. Confirm that the values appear as expected.

A hypothetical lead report might show:

That distinction helps you avoid describing all 370 events as equivalent sales leads.

SourcetoMCP can inspect and register the definitions. Its current GA4 reporting operations use a fixed selection of dimensions and do not accept arbitrary custom-dimension names. Validate and analyse the new custom values in GA4’s reports or explorations.

Investigate missing values before creating another definition

If the report shows (not set), check whether the parameter was sent on the relevant events, whether its spelling matches and whether the chosen scope is correct.

Also check the property and reporting dates. A definition in one property does not apply to another.

Ask your assistant to review the saved configuration against your tracking plan, then test the actual event collection in Analytics.

Start with one marketing question and one dimension. Use SourcetoMCP to check the property’s existing definitions before registering the parameter you need.