diff --git a/js/formats/2mg.js b/js/formats/2mg.js
index 63eb77a..d60c621 100644
--- a/js/formats/2mg.js
+++ b/js/formats/2mg.js
@@ -16,6 +16,11 @@ import ProDOS from './po';
 
 import { numToString, debug } from '../util';
 
+/**
+ * Returns a `Disk` object from a 2mg image.
+ * @param {*} options the disk image and options
+ * @returns {import('./format_utils').Disk}
+ */
 export default function _2MG(options) {
     var OFFSETS = {
         CREATOR: 0x04,
diff --git a/js/formats/block.js b/js/formats/block.js
index 5f0c418..f4f5f24 100644
--- a/js/formats/block.js
+++ b/js/formats/block.js
@@ -9,6 +9,11 @@
  * implied warranty.
  */
 
+/**
+ * Returns a `Disk` object for a block volume with block-ordered data.
+ * @param {*} options the disk image and options
+ * @returns {import('./format_utils').Disk}
+ */
 export default function BlockVolume(options) {
     var { rawData, readOnly, name } = options;
     var disk;
diff --git a/js/formats/nib.js b/js/formats/nib.js
index dee4e1d..91437ad 100644
--- a/js/formats/nib.js
+++ b/js/formats/nib.js
@@ -9,6 +9,11 @@
  * implied warranty.
  */
 
+/**
+ * Returns a `Disk` object from raw nibble image data.
+ * @param {*} options the disk image and options
+ * @returns {import('./format_utils').Disk}
+ */
 export default function Nibble(options) {
     var { data, name, rawData, volume, readOnly } = options;
     var disk = {
diff --git a/js/formats/woz.js b/js/formats/woz.js
index a2d4315..74258f5 100644
--- a/js/formats/woz.js
+++ b/js/formats/woz.js
@@ -184,6 +184,11 @@ function MetaChunk(data) {
     return this;
 }
 
+/**
+ * Returns a `Disk` object from Woz image data.
+ * @param {*} options the disk image and options
+ * @returns {import('./format_utils').Disk}
+ */
 export default function Woz(options) {
     var { rawData } = options;
     var dv = new DataView(rawData, 0);