The more eyes you get on your prototype, the better. With Sketch, you can easily share your prototypes with colleagues and clients — and add comments as you review it, from any web browser.
How to share prototypes
In the prototype’s Preview window, click the Share icon 
in the top-right corner. From there, you can copy a link to the prototype to your clipboard or share it using other apps installed on your Mac, such as AirDrop or email.
When sharing a link, first make sure your prototype is shareable by setting the link’s permissions to View in the document’s Settings.
From the sharing options you can toggle the check boxes to hide Hotspots and hints or the toolbar and navigation, which helps create a more client-friendly and distraction-free experience in your prototype.
Keep in mind that you can only share prototypes from Workspace documents.
How to share a prototype link from the Mac app
Click the Copy Link icon 
on the upper right. From here you can also toggle the check boxes to hide Hotspots and hints, and/or the toolbar and navigation, which helps create a more client-friendly and distraction-free experience in your prototype.
How to share a prototype link from the web app
You can also directly copy and share a prototype’s URL from the Preview window in your browser.
To share a prototype from the iPhone app tap the Share icon in the document’s title when viewing the document sheet.
Commenting on prototypes
Clients or colleagues can comment on your prototypes using only a web browser, which can be a handy way to collaboratively review your work.
To show comments in the Prototype Player, click the Comment icon 
on the upper right. The comments you’ll see here only apply to the currently visible Artboard.
To add new comments, click the 
or press N, drop your comment pin anywhere on the Artboard, and start typing.
When you share a prototype, everyone will see any existing comment threads.
When you comment on an Overlay, you’ll see the comment pin highlighted when you hover over it to show that you’re commenting on a different Artboard.
Once you’ve finished viewing or adding comments, click the Comment icon again to continue interacting with the prototype.
How to view and add comments in a shareable prototype