diff --git a/packages/backend-defaults/config.d.ts b/packages/backend-defaults/config.d.ts
index f0632a37bb..d578a4c510 100644
--- a/packages/backend-defaults/config.d.ts
+++ b/packages/backend-defaults/config.d.ts
@@ -1249,5 +1249,15 @@ export interface Config {
        */
       plugins: string[];
     }>;
+
+    /**
+     * A list of deployed Backstage instances that can be crawled for discovery.
+     */
+    instances: Array<{
+      /**
+       * The base URL of the instance. All /.backstage/ routes should be accessible.
+       */
+      baseUrl: string | { internal: string; external: string };
+    }>;
   };
 }