What Is dateModified? (Schema.org Property)

dateModified is a schema.org property, expressed in ISO 8601 format inside JSON-LD markup, that declares when a page's content last changed. Paired with datePublished, it is the primary machine-readable freshness signal that search and answer engines read when deciding whether a page is current.

Why a single property carries real weight

Answer engines rank and cite time-sensitive content partly by date, and they need a structured field to do it reliably — parsing "Last updated March-ish" from body text is error-prone. Google's documentation on publication dates states that dates should be updated only when meaningful changes occur, and that structured data plus a visible on-page date is the recommended combination. Perplexity and ChatGPT search surface dates directly on source cards, so the value you declare becomes part of your citation's presentation.

How to use it honestly

• Emit dateModified in Article or BlogPosting JSON-LD, matching a visible "Updated on" line the user can see.
• Change it when facts change: refreshed statistics, rewritten sections, corrected errors, new comparisons.
• Do not change it for typo fixes, CSS updates, or CMS re-saves.
• Keep datePublished stable; only dateModified moves.
• Keep the sitemap lastmod value consistent with it, so crawl scheduling and on-page markup tell one story.

Why fake freshness backfires

Engines keep crawl histories. When dateModified advances but a content diff shows near-zero change, the mismatch is detectable and the signal gets discounted — the site's dates lose credibility wholesale, not just on one URL. This is the structured-data equivalent of crying wolf: a site whose every page claims to be updated yesterday gives the engine no way to find the pages that genuinely were.

Example

A glossary of 300 pages runs a quarterly review. In Q2, 41 entries get substantive updates; only those 41 receive new dateModified values and changelog lines. When Perplexity users ask year-qualified questions ("as of 2026"), those refreshed entries carry current dates on their source cards while untouched entries honestly show 2025 — and the site's dates stay trustworthy. Teams doing AI visibility tracking can watch refreshed pages re-enter citation rotations within a crawl cycle or two.

Related terms

See content freshness, Article schema, JSON-LD, content refresh, and sitemap lastmod.