In more detail
A sitemap is usually found at an address such as /sitemap.xml. Each entry gives a URL and, optionally, a lastmod date. Large sites split URLs across several sitemaps and list them in a sitemap index file. Google's sitemaps overview explains when you need one and how to build it.
According to Google, you might need a sitemap if your site is large, new with few external links, or has rich media content. Small, well-linked sites can often be crawled fine without one, though having one rarely hurts.
Good sitemap practice:
- List only canonical, indexable URLs that return a 200 status, not redirects, errors or noindexed pages
- Keep lastmod accurate. Google says it uses lastmod if it's consistently and verifiably accurate
- Respect the limits: up to 50,000 URLs or 50 MB uncompressed per file
- Submit it in Google Search Console and reference it in robots.txt
- Generate it automatically from your CMS so it stays current
Sitemaps can also carry hreflang annotations, and there are extensions for images, video and news.
Search Console's Sitemaps report shows when each sitemap was read and how many URLs it found. Comparing listed URLs with the Page indexing report helps spot pages that are submitted but not indexed.
Why it matters when hiring an agency
Sitemap problems are easy to find and fix, and audits should check them. Common issues include sitemaps full of redirected or noindexed URLs, missing important sections, or dates that change daily for every page.
Be sceptical of anyone offering to "submit your site" to Google or to thousands of search engines for a fee. Submitting a sitemap through Search Console is free, and Google's hiring guide describes mass submission services as "typically useless exercises".