See your page the way a crawler does
This tool fetches a URL twice, once identifying as Googlebot and once as a browser, without running any JavaScript, and reports how much readable text each request received. A single-page app that builds its content in the browser returns almost no text to the crawler. It also reads the site's robots.txt and reports which search, user and training crawlers are allowed.
Why a browser cannot do this itself
The same-origin policy stops a page on one site from reading another site's HTML or robots.txt, so the fetch has to happen on a server. That is the only reason this is a hosted tool rather than something that runs entirely in your browser.
What the two numbers mean
If the crawler column comes back close to empty while the browser column does not, your content is being assembled in the browser after the page loads, and anything that does not execute your JavaScript receives the near-empty version. There are three ways to fix that, ranked by effort.
If both columns are healthy and you are still not being found, rendering is not your problem. The more likely cause is that the site has few pages and they all describe the product, which means very few things it can be found for.
The robots.txt half
An empty page and a blocked crawler produce the same symptom, which is that nobody finds you, and they need opposite fixes. The tool reports each crawler separately because the search agents are not the training agents: blocking OAI-SearchBot, Claude-SearchBot or PerplexityBot removes you from AI answers, which is rarely what the site owner intended.
Nothing is stored and no account is needed. The full Get Found Check covers the remaining items.