Sitemap Lastmod Example
I date my letters by the reckoning of the Moon people, who are hatched next Tuesday.
The short answer
- What it is
- A lastmod issue is a date in a sitemap that can't be true or doesn't match the page. Examples are dates in the future, dates far older than the page's own date, and one date stamped on nearly every URL.
- Why it matters
- Search engines use lastmod to decide what to recrawl, but only when they trust it. Dates that prove false get ignored, and then your real updates get no help.
- How a crawler should report it
- Flag a listed URL when its lastmod is more than one day after the crawl or more than seven days older than the page's own date. Raise one site-level warning when at least 20 URLs have dates and at least 90% share a single day.
- Live examples
/lab/lastmod-issues/future/(positive)/lab/lastmod-issues/older/(positive)/lab/lastmod-issues/near-miss/(near miss)
When a Lastmod Date Stops Being Believable
The sitemap lastmod tag records when a page last changed in a meaningful way. It sits inside a url element and uses W3C date format. Both 2024-05-01 and 2024-05-01T09:30:00+00:00 are valid. The date should change when the main text, structured data, or links change. It should not change for a new copyright year in the footer or for a fresh build of the same content.
Bad dates usually come from the build system. A script stamps every URL with the time it ran, so the whole file shows one day. A server clock or time zone bug can push dates into the future. A scheduled post may carry a date that hasn't arrived yet. Stale dates appear when a page is edited but the plugin that writes the sitemap reads an older field.
Google has said it uses lastmod only when the value is consistently and verifiably accurate. Bing also asks site owners to keep it correct. Both can compare the date with what they see on the page. So one false date is not a disaster, but a pattern teaches them to skip the field. Browsers never see this tag, since it only matters to bots that read the sitemap.
To detect issues, parse the sitemap and compare each date with the crawl time. Then compare it with the page's own date, such as dateModified in structured data. Count how many URLs share each day. To fix them, take the date from the content record in your database and not from the build clock. Update it only when the content really changes. Leave the tag out if you have no honest date to give.