Paste a feed’s XML and check it against the RSS 2.0 and Atom specs, required elements, item structure, and the usual gotchas. Runs in your browser.
A feed that almost-validates will silently break in some readers and not others. This validator parses your XML, detects whether it’s RSS 2.0 or Atom, and checks the structural rules each spec requires, then lists errors (real violations), warnings (recommended-but-missing), and a parsed summary so you can see exactly what a reader would.
<rss> root, a <channel>, and the required
title, link, and description; each <item> needs a
title or description.<feed> root with id, title, and
updated; each <entry> needs the same three.&, mismatched tags, and other XML parse errors.Because it runs in your browser, you paste the XML directly (cross-origin fetching is blocked by browsers), grab it with View Source on the feed URL.
Browsers block reading most cross-origin URLs (CORS), so a purely client-side tool can’t fetch an arbitrary feed. Pasting the XML keeps everything local and private.
An unescaped & in a title or URL, it must be & in XML. That single character breaks the whole document.
Convert a subscription list with the OPML converter, or learn what RSS is.