RSS/Atom Feed Analyzer
While working on RSS Style, I discovered that a lot of RSS/Atom feeds in the wild are (cough) sub-optimal.
The W3C has a Feed Validation Service, but it only looks at the feed itself, not at the linked pages. And a lot of the problems that it finds are about things in the content which can mask more serious errors.
Anyhow, give it a try at https://www.rss.style/feed-analyzer.html.
RSS.Style has a list of high-profile feeds that you can try (and feel better about having problems in your own feed).
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