The sitemap you have, against what is actually linked
Two things at once: it looks for the sitemap the site already publishes, and it follows links from the page you give it — same host only, up to 50 pages or twenty seconds, whichever comes first. Six at a time, which is brisk without being rude to the site.
The file is rarely the answer
Most sites that need a sitemap already have one. WordPress with Yoast or Rank Math publishes an index of several; Shopify and Squarespace publish one and regenerate it on every change. A tool that crawls fifty pages and hands you XML without ever looking for that file is offering a downgrade in the shape of a deliverable — and a sitemap that omits pages is not neutral, it is a statement that the omitted ones do not exist.
So the first thing this does is go and find it. What it hands back when one is there is not a replacement file: it is the list of pages the crawl reached by following links that your sitemap does not mention. That list is usually short, and when it is not, it is usually a plugin that quietly stopped including a post type.
The orphan page is the other output
The comparison runs both ways, and the other direction is worth reading too: open the crawl list next to the pages you believe exist. Anything on your list and not in the crawl is orphaned — reachable only if you already know the URL.
That happens constantly with the exact pages that matter here. Someone writes a comparison page or a detailed FAQ, publishes it, and links it from nowhere. It is in the CMS, it is in the sitemap the plugin generates, and no crawler following links will ever arrive at it with any weight behind it.
Then check whether it can be read at all
A sitemap gets a page found. The AI crawler checker tells you whether the engines are allowed to fetch it, and the metadata checker tells you whether there is any text in it before JavaScript runs.
Questions
See who the engines recommend instead
12 buyer questions across ChatGPT, Perplexity and Gemini. You get the questions your client loses, who won them, and what is missing from the site. No score, no signup wall.