Here are some free RSS validator:
- W3C validator: W3C validator is for syndicated feeds. It supports validate by URI and also validate by direct Input. W3C feed validator works with RSS
0.90,0.91,0.92,0.93,0.94,1.0, and2.0. Enter the address of your feed or XML content and click “validate.” Errors will be highlighted, with messages for each problem. - RssBoard Feed Validator: It only support validat by URI, Enter the URL of an RSS feed for quick validation.
- Podbase: For podcast feeds. Podbase will check your URL, make sure your XML is well formed, and whether it is iTunes-compatible. It will also check for things like your cover art being in iTunes compliance, correct category, correct summary, and more.
- Cast Feed Validator: For podcast feeds. This validates your feed, checks the main image, as well as media files, while letting you visualize your podcast RSS feed.
- Feed Validator: Feed Validator is for Atom, RSS, and KML feeds. Like W3C, it also gives you highlighted errors with messages and information for each problem found.
References: