Atom

Atom is a web feed/syndication format intended to replace RSS. Its creation was motivated by a desire to have an open, standardized feed format free from the confusion of the various incompatible RSS versions. Atom has been documented in several RFC documents through the IETF (an Internet standards body), and has an officially-registered MIME type (unlike RSS), but has yet to gain the broad use and acceptance RSS has.

Like RSS, Atom is XML-based, and its basic syntax is very similar; however, some of the element names are different. Resolving one of the ambiguities of RSS, Atom permits the explicit declaration of the content type and encoding format of feed content, whereas RSS leaves the reader guessing whether the contents of a feed are intended to be interpreted as plain text or HTML.

The h-feed and h-entry (formerly collectively known as hAtom) "microformats" allow a subset of Atom to be encoded within an HTML or XML document.

Format specs

 * RFC 4287 - main document
 * RFC 5023 - publishing protocol
 * RFC 4685 - threading extensions
 * RFC 5005 - paging and archiving
 * hAtom - microformat for marking up HTML for an Atom feed

Validators

 * Feed Validator - validates various RSS and Atom versions

Other links

 * Atom Wiki
 * Wikipedia article