diff --git a/src/type.ts b/src/type.ts
new file mode 100644
index 0000000..97cf9a7
--- /dev/null
+++ b/src/type.ts
@@ -0,0 +1,58 @@
+import type { IO, UnderlyingFileSystem } from "@miyauci/file-system";
+
+export interface FilePickerOptions {
+  types?: FilePickerAcceptType[];
+  excludeAcceptAllOption?: boolean;
+
+  id?: string;
+
+  startIn?: StartInDirectory;
+}
+
+export interface FilePickerAcceptType {
+  description?: string;
+
+  accept: Record<string, string | string[]>;
+}
+
+export interface DirectoryPickerOptions {
+  id?: string;
+  startIn?: StartInDirectory;
+  mode?: FileSystemPermissionMode;
+}
+
+export type WellKnownDirectory =
+  | "desktop"
+  | "documents"
+  | "downloads"
+  | "music"
+  | "pictures"
+  | "videos";
+
+export type FileSystemPermissionMode = "read" | "readwrite";
+
+export type StartInDirectory = WellKnownDirectory | FileSystemHandle;
+
+export interface FileSystemPermissionDescriptor extends PermissionDescriptor {
+  handle: FileSystemHandle;
+  mode: "read" | "readwrite";
+}
+
+export interface OpenFilePickerOptions extends FilePickerOptions {
+  multiple?: boolean;
+}
+
+export interface OpenDirectoryPicker {
+  (options?: DirectoryPickerOptions): { root: string };
+}
+
+export interface OpenFileDialog {
+  (options?: OpenFilePickerOptions): { root: string; name: string }[];
+}
+
+export interface Adaptor {
+  openFileDialog: OpenFileDialog;
+  openDirectoryDialog: OpenDirectoryPicker;
+  fs: UnderlyingFileSystem;
+  io: IO;
+}