RSS & Atom cheat sheet

A scannable RSS & Atom reference: 10 short snippets across 8 topics, each linking back to the lesson it came from.

At a glance

Quick snippets

The RSS 2.0 feed format

The details readers rely on

<item>
  <title>Episode 12: Shipping small</title>
  <enclosure url="https://cdn.example.com/ep12.mp3" length="48213004" type="audio/mpeg"/>
  <category>engineering</category>
  <author>[email protected] (Platform Team)</author>
  <comments>https://example.com/posts/ep12#comments</comments>
</item>

Full lesson: The RSS 2.0 feed format →

Generating a valid feed

Validate and serve correctly

# well-formedness, then structure against the RSS 2.0 schema
xmllint --noout feed.xml
curl -sSL https://www.rssboard.org/files/schema.rng -o rss.rng
xmllint --noout --relaxng rss.rng feed.xml

# check what the reader will actually see
curl -sSI https://example.com/feed.xml | grep -i content-type
curl -s https://example.com/feed.xml | xmllint --format - | head -30

Validate and serve correctly

HTTP/1.1 200 OK
Content-Type: application/rss+xml; charset=utf-8
Cache-Control: max-age=300
ETag: "feed-2026-09-18-01"
Last-Modified: Fri, 18 Sep 2026 09:00:00 GMT

Validate and serve correctly

<link rel="alternate" type="application/rss+xml"
      title="Example Dev Blog" href="https://example.com/feed.xml"/>

Full lesson: Generating a valid feed →

Atom and how readers consume feeds

How a reader actually polls

# emulate a reader: fetch, remember the validator, then revalidate
curl -sSI https://example.com/feed.xml | grep -iE 'etag|last-modified'

curl -sS -o /dev/null -w '%{http_code}\n' \
  -H 'If-None-Match: "feed-2026-09-18-01"' \
  https://example.com/feed.xml          # expect 304

# aggregate feeds are frequently rate limited - honour Retry-After
curl -sSI https://example.com/feed.xml | grep -i retry-after

Full lesson: Atom and how readers consume feeds →

Choosing a feed format: RSS 2.0, Atom and JSON Feed

One item model, several serialisers

<!-- Atom benefit in practice: the date is unambiguous and required -->
<entry>
  <id>https://example.com/releases/2026-09-platform-3-2</id>
  <title>Platform 3.2</title>
  <updated>2026-09-18T09:00:00+01:00</updated>
  <author><name>Platform Team</name></author>
  <link rel="alternate" href="https://example.com/releases/2026-09-platform-3-2"/>
  <summary>Streaming transforms and faster cold start.</summary>
  <content type="html">&lt;p&gt;Streaming transforms and faster cold start.&lt;/p&gt;</content>
</entry>

Full lesson: Choosing a feed format: RSS 2.0, Atom and JSON Feed →

Podcast feeds and the Apple and Podcasting 2.0 tags

Identifiers that survive a re-host

# A podcast guid must not depend on anything you might change later.
BAD = "https://cdn.example.com/audio/ep41.mp3"   # breaks if you move the CDN
BAD2 = "Episode 41: Cold starts"                 # breaks if you fix a typo in a title
GOOD = "urn:example:podcast:shipping-it:ep-41"   # opaque, permanent, ours

# If the feed moves to a new host, the <podcast:guid> of the channel should
# stay put too, so directories recognise it as the same show.
CHANNEL_GUID = "9f2b1c4d-1111-2222-3333-abcdef012345"

Full lesson: Podcast feeds and the Apple and Podcasting 2.0 tags →

Validating and troubleshooting feeds

The checks worth automating

# Validate in the build, so a broken feed never reaches subscribers
import subprocess, sys

def build_and_check(path: str) -> None:
    xml = render_feed()
    open(path, "w", encoding="utf-8").write(xml)
    r = subprocess.run(["xmllint", "--noout", path], capture_output=True, text=True)
    if r.returncode != 0:
        print(r.stderr, file=sys.stderr)
        raise SystemExit("feed is not well-formed XML")

Full lesson: Validating and troubleshooting feeds →

Feed security: sanitising third-party content

Rendering safely

Content-Security-Policy: default-src 'none'; img-src https: data:; style-src 'unsafe-inline'; base-uri 'none'; form-action 'none'; frame-ancestors 'none'

Full lesson: Feed security: sanitising third-party content →

Feeds at scale: pagination, archives and pipelines

Generating and serving incrementally

GET /feed.xml HTTP/1.1
If-None-Match: "412:2026-09-18T09:00:00+00:00"

HTTP/1.1 304 Not Modified
ETag: "412:2026-09-18T09:00:00+00:00"
Cache-Control: public, max-age=300
Content-Type: application/rss+xml; charset=utf-8

Full lesson: Feeds at scale: pagination, archives and pipelines →

FAQ

Related cheat sheets

XML XPath XSLT SOAP RESTful APIs

Last refreshed 2026-09-27.