Sitemap Protocol

The sitemap protocol is the open standard, published at sitemaps.org and supported by Google, Bing, and others, that defines how a sitemap must be structured. It specifies the XML schema, the required <urlset> and <url> elements with <loc>, and the optional <lastmod>, <changefreq>, and <priority> tags.

The protocol also sets hard limits: a single sitemap file may contain at most 50,000 URLs and must be no larger than 50MB uncompressed. Files exceeding either limit must be split and tied together with a sitemap index. All URLs in one sitemap should share the same host, and each <loc> must be a fully qualified, properly escaped URL.

Following the protocol precisely is what makes a sitemap portable across search engines. Extensions for images, video, and hreflang build on the same base schema, so a valid core sitemap is the foundation for everything else.