What Google does with lastmod — and why it ignores priority and changefreq

A sitemap has three optional fields per URL. Google uses one and discards the other two. Knowing which is which keeps you from spending effort on what changes nothing.

lastmod: a signal, when it is honest

lastmod states when that URL's content last changed. Google treats it as a hint for prioritizing re-crawling — but only while the value stays trustworthy. If every page carries today's date on each generation, the signal stops meaning anything and Google ignores it for the whole site. The date is worth more left out than faked: fill it only when it reflects a real change, in W3C datetime format.

priority and changefreq: ignored

priority never influenced ranking and does not tell Google which page matters more — relative importance is inferred from links and content, not from a number you write yourself. changefreq was a promise about how often a page changes that the crawler never honored: it sets its visit rhythm from the page's actual history. Google states publicly that it ignores both. They remain valid in the XML for compatibility, but they move nothing.

What GenMap does

The crawl derives lastmod from each page's real modification date — the Last-Modified header, article metadata, the lastmod of a seed sitemap — and omits it when there is no reliable date, rather than inventing one. It is the opposite of stamping everything with today.