What is the difference between a sitemap and a sitemap index?

A sitemap is a urlset listing individual page URLs. A sitemap index is a sitemapindex listing other sitemap files. You need an index when a single sitemap would exceed 50,000 URLs or 50 MB uncompressed, splitting the URLs across multiple child sitemaps.

Are changefreq and priority still used by Google?

Google has stated it largely ignores changefreq and priority — it relies on its own crawl signals. They remain valid protocol elements and some other crawlers read them, but do not expect them to influence Googlebot. lastmod, when accurate, is the hint Google does pay attention to.

What format must lastmod use?

lastmod uses W3C Datetime / ISO 8601 — either a date like 2026-06-06 or a full timestamp like 2026-06-06T14:30:00+00:00. Keep it accurate; a lastmod that never matches real changes is treated as untrustworthy and may be ignored.

What are the size limits for a sitemap file?

A single sitemap may contain at most 50,000 URLs and must be no larger than 50 MB uncompressed. If either limit is reached, split into multiple sitemaps and reference them from a sitemap index, which itself may list up to 50,000 sitemaps.

How do search engines find my sitemap?

Reference it in robots.txt with a Sitemap: line pointing to the absolute URL, and/or submit it in Google Search Console and Bing Webmaster Tools. The file must live on the host it covers and all loc URLs must share that host and scheme.

Sitemap Protocol Reference

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The XML Sitemap Protocol

A sitemap is an XML file that lists a site’s URLs so crawlers can discover and prioritise them. The protocol defines a small set of elements — urlset, url, loc, lastmod, changefreq, priority — plus a sitemapindex format for large sites and extensions for images, video and news. This reference lists each element with its meaning, format and constraints.

How it works

A basic sitemap wraps URL entries in a namespaced urlset:

<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
  <url>
    <loc>https://example.com/</loc>
    <lastmod>2026-06-06</lastmod>
    <changefreq>weekly</changefreq>
    <priority>1.0</priority>
  </url>
</urlset>

When you exceed 50,000 URLs or 50 MB, split the file and list the parts in an index:

<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
  <sitemap>
    <loc>https://example.com/sitemap-1.xml</loc>
    <lastmod>2026-06-06</lastmod>
  </sitemap>
</sitemapindex>

Reference the file from robots.txt and submit it in Search Console.

Tips and notes

loc is the only required child of url; everything else is optional.
All loc URLs must share the host and scheme of the sitemap’s location.
lastmod is the hint Google actually uses — keep it truthful; changefreq and priority are largely ignored by Googlebot.
Limits: 50,000 URLs and 50 MB uncompressed per file; gzip-compress large files.
Extensions add namespaces: image:image, video:video, and news:news for Google News (which expects entries within ~2 days of publication).