What a sitemap is actually for

A sitemap does not make pages rank. It is a discovery aid: a plain list telling search engines which URLs you consider canonical and worth looking at. On a small site with clean internal linking it changes very little. On a large site, a new site, or one with pages that are not well linked internally, it is the difference between being found this week and being found next quarter.

The rules are simple. One file holds at most 50,000 URLs and must be under 50 MB uncompressed. Every URL must be absolute, must use the same protocol and hostname as the sitemap file itself, and should return a 200 status. If you need more than 50,000 URLs, split the list and reference each file from a sitemap index.

Be honest about lastmod

Google has said publicly that it uses the lastmod value only when it is consistently accurate. Sites that stamp today’s date on every URL at every rebuild teach crawlers to ignore the field entirely. If you cannot generate a real modification date, leave it out — an absent field is better than a misleading one.

priority and changefreq are largely ignored by Google these days. They do no harm, but do not expect them to move anything.

What to leave out

Keep noindexed pages, redirects, canonicalised duplicates, paginated archives and tag pages out of the file. A sitemap full of URLs that resolve to something else is a signal that your list is not maintained, and it wastes the crawl budget you were trying to direct.