diff --git a/index.d.ts b/index.d.ts
index f518be4a..65c68239 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -207,7 +207,12 @@ declare namespace hapiswagger {
     /**
      * A function used to determine which tags should be used for grouping (when `grouping` is set to `tags`)
      *
+     * @remarks
+     * @link https://swagger.io/specification/#tagObject
+     *
+     *
      * @param tag - String used to group API endpoint
+     * @returns True or false
      *
      * @example
      * ```
diff --git a/index.test-d.ts b/index.test-d.ts
index ee184c4d..366129f5 100644
--- a/index.test-d.ts
+++ b/index.test-d.ts
@@ -19,7 +19,7 @@ import * as hapiswagger from '.';
           email: 'who@where.com'
         }
       },
-      tagsGroupFilter: tag => tag !== 'api'
+      tagsGroupFilter: (tag: string) => tag !== 'api'
     }
   });