I was curious about what the difference between RSS and Atom was. This blog post is a small primer to RSS and Atom feeds and describes the differences between both. I’ve linked links to the technical specification at the end of this post.

General

RSS (Really Simple Syndication) and Atom are often used interchangeably, and most feed readers can process both formats. Both use an open dialect of XML, which is computer-readable and allows feed-/RSS-/Atom readers to subscribe to a feed and pull new content to the client. RSS was released in 1999, and Atom followed a little bit later in 2005. The Harvard university specified RSS with the current version of 2.0, Atom is an IETF standard, and the current version is 1.0.

Those feeds provide a privacy-friendly way to consume the content. The content provider can’t track the behavior on your feed reader, and most tracking methods do not work either.

The most common use case is to stay up-to-date on blogs/news sites and podcasts. But you can use RSS for even more: e.x. stay up-to-date on your favorite Youtube videos without an account. Simply visit the Youtube channel, open the homepage source code, and search for rssURL. Just copy the link like this https://www.youtube.com/feeds/videos.xml?channel_id=UCW6xlqxSY3gGur4PkGPEUeA into your feed reader, and you get notified when a new video is being published.

RSS uses either .rss or .xml as file extension, and Atom uses .atom or .xml.

Main differences

In general: RSS has a broader adoption, but Atoms provides more features. I will try to describe some of them.

Content payloads

RSS only provides escaped HTML or plain text. Atom can provide various types of content within the same payload.

Atom is therefore recommended for more complex content.

Internationalization

RSS provides internationalization at the feed level and Atom at every individual element level. This means that you only need one feed per language for RSS and only one link for all languages for Atom. Furthermore, Atom provides better support for international characters.

Markdown format

RSS does not support custom XML markup. Almost all text formatting is getting lost, and is especially in long-format text content troublesome since it hinders accessibility. It is recommended to use Atom if you want to preserve as much formatting as possible.

Autodiscovery

Both support autodiscovery which allows browsers and feed readers to automatically detect the RSS feed.

RSS:

<link rel="alternate" type="application/rss+xml" 
  title="The Title of your blog or whatever" 
  href="/rss/" />

Atom:

<link rel="alternate" type="application/atom+xml." 
  title="The Title of your blog or whatever" 
  href="/rss/" />

Implementation

Without having worked on them: Atom seems easier to work with since the code is reusable and more strict, and RSS is less strict but a bit more complex. I won’t be able to quantify this, but I’ve read this multiple times.