RSS Validators
If you don’t use a proven tool to generate your RSS feed, you need a way to check that your feed is compliant with the RSS specification, and that most other tools will be able tor read it.
Feed Validator
Based on an Open Source by Sam Ruby, Mark Pilgrim, Joseph Walton and Phil Ringnalda. It supports Really Simple Syndication (RSS) and two other syndication formats in wide usage today: Atom and RDF Site Summary.
RSS Validator
Uses the same code as Feed Validator above.
Feed Validation Service
Brought to you by w3.org. Supports both RSS or Atom Feeds. The onwers of the RSS specification.