In addition to consuming feeds, you may want to create feeds as part of your mashups. It’s certainly helpful to read and understand the specifications for the various feed formats. I have found the following feed validators to be invaluable in helping me to spot and correct errors in feeds that I create or read from others:
http://feedvalidator.org is an online service, whose software you can also run locally.[83]
http://validator.w3.org/feed/ is a W3C service built from the software available at http://feedvalidator.org. The syntax checking is available also as a SOAP web service.[84][85]
For dealing with RSS 1.0, you may find the W3C RDF Validation Service useful (http://www.w3.org/RDF/Validator/).