For AI agents: llms.txt is a short guide that sends you to the rules your problem needs, and rules.json holds every rule of this playbook as JSON.

How to do it

Take both dates from the page data, so the visible date, the JSON-LD and the sitemap lastmod agree. Change dateModified only when the main content changes, never on every build. Give a time zone with any time, in the format Send dates as RFC 3339 with a time zone uses. Keep other dates on the page to a minimum, so search engines pick the right one.

Examples

Using these examples: they show one way to follow this rule. Keep the behaviour and the check, not the syntax. Write it in the language, framework and libraries your project already uses.

HTML example

<p>Updated <time datetime="2026-09-14">14 September 2026</time></p>
<script type="application/ld+json">
{ "@context": "https://schema.org", "@type": "Article", "headline": "How to care for oak floors",
  "datePublished": "2026-03-02T09:00:00+01:00", "dateModified": "2026-09-14T10:30:00+02:00" }
</script>

JavaScript example

const visible = page.querySelector('time[datetime]').getAttribute('datetime');
const { dateModified } = JSON.parse(page.querySelector('script[type="application/ld+json"]').textContent);
assert.equal(dateModified.slice(0, 10), visible);
assert.equal(sitemapLastmod[url], visible);

Python example

visible = page.select_one("time[datetime]")["datetime"]
date_modified = json.loads(page.select_one('script[type="application/ld+json"]').string)["dateModified"]
assert date_modified[:10] == visible == sitemap_lastmod[url]

How to check

A build test reads each article. Its visible <time datetime> equals datePublished or dateModified, dateModified equals the sitemap lastmod, and no date is later than the build.

Sources

• Google Search Central – Influence the byline date

Related rules

• Send dates as RFC 3339 with a time zone in API design