diff --git a/index.d.ts b/index.d.ts
index dce415d..77e444c 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -193,6 +193,14 @@ interface FsPackage {
         bytes: boolean // if true return []byte instead of string
     }): string | any
 
+    /**
+     * write data to a file relative to config dir
+     *
+     * @param path relative file path
+     * @param data string or []byte data
+     */
+    writeFile(path: string, data: string|any): null
+
     /**
      * stat file or directory
      *