diff --git a/packages/frontend-app-api/src/extensions/Core.tsx b/packages/frontend-app-api/src/extensions/Core.tsx
index cb93b2888f..4cb21a8702 100644
--- a/packages/frontend-app-api/src/extensions/Core.tsx
+++ b/packages/frontend-app-api/src/extensions/Core.tsx
@@ -17,17 +17,16 @@
 import {
   coreExtensionData,
   createExtension,
+  createExtensionInput,
 } from '@backstage/frontend-plugin-api';
 
 export const Core = createExtension({
   id: 'core',
   at: 'root',
   inputs: {
-    apis: {
-      extensionData: {
-        api: coreExtensionData.apiFactory,
-      },
-    },
+    apis: createExtensionInput({
+      api: coreExtensionData.apiFactory,
+    }),
   },
   output: {},
   factory() {},
diff --git a/packages/frontend-app-api/src/extensions/CoreLayout.tsx b/packages/frontend-app-api/src/extensions/CoreLayout.tsx
index 29680bf23c..0c5c0446fc 100644
--- a/packages/frontend-app-api/src/extensions/CoreLayout.tsx
+++ b/packages/frontend-app-api/src/extensions/CoreLayout.tsx
@@ -18,6 +18,7 @@ import React from 'react';
 import {
   createExtension,
   coreExtensionData,
+  createExtensionInput,
 } from '@backstage/frontend-plugin-api';
 import { SidebarPage } from '@backstage/core-components';
 
@@ -25,39 +26,28 @@ export const CoreLayout = createExtension({
   id: 'core.layout',
   at: 'root',
   inputs: {
-    nav: {
-      extensionData: {
+    nav: createExtensionInput(
+      {
         element: coreExtensionData.reactElement,
       },
-    },
-    content: {
-      extensionData: {
+      { singleton: true },
+    ),
+    content: createExtensionInput(
+      {
         element: coreExtensionData.reactElement,
       },
-    },
+      { singleton: true },
+    ),
   },
   output: {
     element: coreExtensionData.reactElement,
   },
   factory({ bind, inputs }) {
-    // TODO: Support this as part of the core system
-    if (inputs.nav.length !== 1) {
-      throw Error(
-        `Extension 'core.layout' did not receive exactly one 'nav' input, got ${inputs.nav.length}`,
-      );
-    }
-    if (inputs.content.length !== 1) {
-      throw Error(
-        `Extension 'core.layout' did not receive exactly one 'content' input, got ${inputs.content.length}`,
-      );
-    }
-
     bind({
-      // TODO: set base path using the logic from AppRouter
       element: (
         <SidebarPage>
-          {inputs.nav[0].element}
-          {inputs.content[0].element}
+          {inputs.nav.element}
+          {inputs.content.element}
         </SidebarPage>
       ),
     });
diff --git a/packages/frontend-app-api/src/extensions/CoreRoutes.tsx b/packages/frontend-app-api/src/extensions/CoreRoutes.tsx
index 5a6cd87bfd..0d20abfb6b 100644
--- a/packages/frontend-app-api/src/extensions/CoreRoutes.tsx
+++ b/packages/frontend-app-api/src/extensions/CoreRoutes.tsx
@@ -18,6 +18,7 @@ import React from 'react';
 import {
   createExtension,
   coreExtensionData,
+  createExtensionInput,
 } from '@backstage/frontend-plugin-api';
 import { useRoutes } from 'react-router-dom';
 
@@ -25,13 +26,11 @@ export const CoreRoutes = createExtension({
   id: 'core.routes',
   at: 'core.layout/content',
   inputs: {
-    routes: {
-      extensionData: {
-        path: coreExtensionData.routePath,
-        ref: coreExtensionData.routeRef,
-        element: coreExtensionData.reactElement,
-      },
-    },
+    routes: createExtensionInput({
+      path: coreExtensionData.routePath,
+      ref: coreExtensionData.routeRef,
+      element: coreExtensionData.reactElement,
+    }),
   },
   output: {
     element: coreExtensionData.reactElement,
diff --git a/plugins/graphiql/src/alpha.tsx b/plugins/graphiql/src/alpha.tsx
index 3d1bf839af..9cd956fc1a 100644
--- a/plugins/graphiql/src/alpha.tsx
+++ b/plugins/graphiql/src/alpha.tsx
@@ -19,6 +19,7 @@ import {
   createApiExtension,
   createExtension,
   createExtensionDataRef,
+  createExtensionInput,
   createNavItemExtension,
   createPageExtension,
   createPlugin,
@@ -64,11 +65,9 @@ const endpointDataRef = createExtensionDataRef<GraphQLEndpoint>(
 export const graphiqlBrowseApi = createApiExtension({
   api: graphQlBrowseApiRef, // apis.plugin.graphiql.browse
   inputs: {
-    endpoints: {
-      extensionData: {
-        endpoint: endpointDataRef,
-      },
-    },
+    endpoints: createExtensionInput({
+      endpoint: endpointDataRef,
+    }),
   },
   factory({ inputs }) {
     return createApiFactory(