# Sitemap Validator > Agent-friendly Markdown of https://www.buildseo.org/free-tools/sitemap-validator — full index for AI agents: https://www.buildseo.org/llms.txt Validate an XML sitemap's structure, URLs, and freshness fields. ## How it works Enter your sitemap URL — or any page on the site and the validator finds /sitemap.xml itself. It checks the XML structure against the sitemaps.org schema, follows a sitemap index one level deep, and counts every URL entry. Every `` value is validated as a real W3C datetime, and up to ten listed URLs are sample-checked live so a sitemap full of 404s gets caught before crawlers lose trust in it. The full result — structure, counts, date problems, and dead sampled URLs — downloads as CSV or JSON, free and instant. ## Frequently asked questions ### Does it handle sitemap index files? Yes. A `` is followed one level deep: the child sitemaps are fetched and their URL entries validated together, with analysis capped at the first 2,000 entries so huge sites still finish fast. ### Why do lastmod dates matter? Search engines use `` to prioritize recrawling — but only when the dates are trustworthy. Invalid formats get ignored, and dates that never change teach crawlers to ignore the whole field. ### What does the sample check actually do? Up to ten URLs spread across the sitemap are requested live. Any that fail to return a 2xx response are listed with their status, because sitemaps that advertise dead pages erode crawler confidence in every other entry. ## Sitemap clean. Now earn the crawl budget. BuildSEO AI builds the verified backlinks that make crawlers care about your sitemap. --- [All free tools](https://www.buildseo.org/free-tools.md) · [BuildSEO AI](https://www.buildseo.org/index.md)