Is there a web viewer for photos stored on iCloud? [duplicate]

Not at the moment. To view your Photo Stream you need to access it on an Apple device (Mac, iOS or Apple TV) that's signed in with your iCloud ID. iCloud.com doesn't offer any functionality to view the Photo Stream, and it seems unlikely to any time soon.

You can also use iPhoto to see this PhotoStream.
You can activate it in the left sidebar or in the your Mac preferences under 'iCloud'.

That's how I see my photos in the iCloud on my Mac. Unfortunately, it's limited to the last 30 days, so not all your iCloud photos will appear in this list. But it's rather easy to create different albums from your PhotoStream to you Mac!