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Atom 1.0

<updated>

When a feed or entry last changed meaningfully, as a strict RFC 3339 timestamp — the other half of the date confusion between Atom and RSS.

Atom requires RFC 3339: 2026-08-10T09:00:00Z, or with an explicit offset. A date alone is not valid, a time without an offset is not valid, and RSS's RFC 822 form is certainly not valid. It is required on the feed and on every entry.

The specification says <updated> should change only when the change is significant, which is a judgement the publisher has to make. Bumping it on every build is the Atom equivalent of stamping every sitemap URL with the deploy time.

Format
Atom 1.0
Namespace
Atom Syndication Format 1.0
Parent
<feed><entry>
How many
Exactly one per <feed> and per <entry>.

What it contains

Nothing — this element holds a value rather than other elements. Its content is text, and the constraints below are what that text has to be.

Cardinality and constraints

Exactly one per <feed> and per <entry>.

  • RFC 3339, with a timezone: 2026-08-10T09:00:00Z or 2026-08-10T09:00:00+02:00.
  • A date alone, or a time with no offset, is invalid.
  • Should change only on a meaningful edit, not on every rebuild.

What our validator does

Every <updated> — the feed's own and each entry's — is matched against the RFC 3339 pattern, and failures are errors rather than warnings.

Broken and fixed

Both documents below are well-formed XML — that is the point of this corpus — and both are run through the validator on every test run. The verdicts here are what it returned, not what we expect it to.

broken
<?xml version="1.0" encoding="UTF-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">
  <id>urn:uuid:60a76c80-d399-11d9-b93c-0003939e0af6</id>
  <title>Example</title>
  <updated>2026-08-10</updated>
  <author><name>Ada Lovelace</name></author>
  <entry>
    <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
    <title>Hen lays egg</title>
    <updated>2026-08-10T09:00:00Z</updated>
  </entry>
</feed>
<feed><updated> is "2026-08-10", which is not RFC 3339. Atom dates are strict: 2026-07-20T09:00:00Z.
fixed
<?xml version="1.0" encoding="UTF-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">
  <id>urn:uuid:60a76c80-d399-11d9-b93c-0003939e0af6</id>
  <title>Example</title>
  <updated>2026-08-10T09:00:00Z</updated>
  <link rel="self" href="https://example.com/feed.xml"/>
  <author><name>Ada Lovelace</name></author>
  <entry>
    <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
    <title>Hen lays egg</title>
    <updated>2026-08-10T09:00:00Z</updated>
  </entry>
</feed>
No errors. Warnings may remain — a conforming feed can still be missing a self link — but nothing here is wrong.

Where it reaches

Related elements

All 34 elements

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