A podcast directory or feed reader told you your feed is "invalid" and nothing else. rssdiag fetches it, parses it the way a real reader would, and tells you exactly what's broken and why it matters — in plain language, with no jargon.
Three steps to a clear answer.
rssdiag checks one feed at a time. It does not crawl your site, download media, or submit to directories. It looks at your feed, reports what it finds, and stops.
The same validations a feed reader performs — reported clearly.
Is the URL valid? Is the feed reachable? Does it return the right HTTP status?
Served with an XML content type — or misconfigured as text/plain?
Does the XML declaration match the Content-Type charset? A mismatch can garble non-ASCII characters.
Is the feed well-formed? Do opening and closing tags balance?
RSS 2.0 or Atom 1.0 — or an unrecognised format that readers will reject.
Missing or duplicate GUIDs, missing titles, missing links, unparseable dates — each flagged with its consequence.
If you publish a feed and got a rejection notice, this tool is for you.
Your podcast directory rejected your feed. You need to know why — fast — without reading a spec document.
Your RSS feed isn't showing new issues in readers. A missing GUID or bad date is usually the culprit.
You maintain a feed but don't have a technical person to hand. rssdiag speaks your language.