Atom (web feed) — format and publishing protocol

Structure and common elements

An Atom feed is structured XML with a defined set of elements that describe the feed itself and each entry it contains. Typical elements include feed metadata (title, id, updated), one or more entry elements, and per-entry fields such as id, title, author, updated, summary and content. Links with rel attributes are used to point to alternate representations or related resources.

• Feed-level: title, id, updated, author
• Entry-level: id, title, updated, summary, content, links
• Metadata: categories, contributors, rights

AtomPub: the publishing protocol

The Atom Publishing Protocol uses HTTP methods (GET, POST, PUT, DELETE) together with collections and entry resources to provide a standardized way to publish and modify feed entries. A client can POST a new entry to a collection, PUT to update an existing entry, or DELETE to remove it. AtomPub complements the syndication format by specifying the interactions between authoring tools and servers.

History and standards

Atom was developed as an alternative to earlier feed formats with the goals of clearer semantics and a better-defined extensibility model. It was standardized through Internet standards processes and is commonly served with the MIME type application/atom+xml. The format was adopted widely because of its namespace support and explicit identifiers for entries.

Uses, examples and distinctions

Atom feeds are used for distributing blog posts, news updates, podcasts, scholarly article alerts and any regularly updated content. Compared with older feed formats, Atom provides precise element meanings, richer metadata, and a companion protocol for remote publishing. Implementations exist in many blogging platforms, content management systems and libraries for parsing and generation.

For technical details and the official specification see the Atom specification, and for general information about syndication formats and how feeds are consumed see web feed resources.