diff --git a/index.d.ts b/index.d.ts
new file mode 100644
index 0000000..7a71c4d
--- /dev/null
+++ b/index.d.ts
@@ -0,0 +1,10 @@
+export interface Range {
+    unit?: string;
+    first?: number | string;
+    last?: number| string;
+    length?: number | string;
+  }
+
+declare function format(obj: Range): string;
+
+export default format;
\ No newline at end of file