Are your publish and update dates written in a format AI can actually read?
Confirms every date in your structured data is in the unambiguous ISO format with a timezone.
What this signal tests
We check every date field your structured data emits, such as when an article was published, when it was last updated, when a video was uploaded, or when an event begins, and verify each one uses the international ISO 8601 standard with a timezone offset. This format looks like 2026-05-22T14:30:00+00:00 and is unambiguous worldwide.
Why it matters for your visibility in AI
Dates without a timezone are ambiguous by twenty-four hours and dates in human-friendly formats like May 22, 2026 are unreliable to parse at scale. AI tools that cannot parse your dates either drop your content from time-sensitive answers or assign it a default date, which is usually older than reality. Either outcome hurts your visibility. The dateModified field matters most. AI answer engines actively prefer fresher sources for evergreen questions, and they use dateModified to decide which version of a competing claim is current. A correctly-formatted dateModified that reflects a recent revision is often the difference between being cited as the up-to-date source and being skipped as stale.
Pass criteria at a glance
| Criterion | Passes when |
|---|---|
| 100% of date fields parse as ISO 8601 with TZ. |
How we test it
We collect every date field present in your structured data blocks across a sample of pages. For each one, we test that it matches the ISO 8601 pattern and includes a timezone (either an offset like +01:00 or the Z suffix for UTC). We also check that dateModified is not earlier than datePublished, which is a common bug. Any failure on any sampled page fails the signal.
Show technical detection method
Regex-validate every date field against ISO 8601 with TZ; assert dateModified >= datePublished.
If your site fails: how to fix it
- Audit how your CMS or codebase formats dates when emitting structured data. Most date bugs come from one helper function that strips the timezone or formats dates locally.
- Switch to your platform's ISO 8601 formatter. In WordPress this is the get_the_date with the c format; in modern JavaScript it is Date.prototype.toISOString or temporal.toString; in Python it is datetime.isoformat with a timezone-aware datetime.
- Make sure dates are stored as timezone-aware datetimes in your database, not naive strings. Most date bugs originate at storage, not output.
- Confirm dateModified is recalculated when content is meaningfully updated and that it never sits earlier than datePublished after a rewrite.
- Spot-check sample articles in Google's Rich Results Test. The test will flag any malformed datetimes immediately.
Quick facts
| Maturity | ESTABLISHED |
|---|---|
| Weight | medium |
| Category | Structured Data |
Primary sources
Related signals
Frequently asked questions
What is wrong with formatting dates as something readable like May 22, 2026?
Human-readable formats are ambiguous and vary by locale. May 22 in the US is 22 May in the UK, and many international parsers swap the day and month. AI tools cannot reliably interpret human formats at scale, so they default to ignoring them. ISO 8601 is the only format that is unambiguous worldwide.
Is just a date like 2026-05-22 enough, or do I need the time and timezone?
A date alone is acceptable for fields that genuinely have no time, such as a publication day. For datetime fields like dateModified or event startDate, include the full datetime with a timezone offset. Where in doubt, include the time and timezone; it never hurts and resolves edge cases at day boundaries.
Why does dateModified need to be later than datePublished?
If your modified date is earlier than your published date, the data is logically broken: you cannot update something before it exists. AI tools and validators treat this as a sign of buggy markup and may downweight or ignore the whole structured data block. Fixing it is usually a one-line change in your template.
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