A quick weight check, not a full audit
This measures how long your HTML took to arrive, then checks the size of the images, scripts, and stylesheets your page links to, adding them up into an estimated total page weight - a reasonable quick proxy for load time, since page weight is one of the biggest drivers of how fast a page feels.
Why this isn't a full Lighthouse-style audit
This does not measure rendering time, JavaScript execution cost, or give you prioritized fix recommendations. For that level of detail, use the PageSpeed Insights Checker tool, which calls Google's actual Lighthouse engine - what this tool gives you instead is a faster, lighter first-pass check of the biggest obvious contributor to slow pages: how much has to download before the page can render.
Why resource counts matter alongside total weight
Breaking weight down by images, scripts, and stylesheets separately helps pinpoint where the bulk is coming from - a page with a reasonable total weight but an unusually high script count often points to too many third-party widgets or tracking tags, while high image weight usually means images that haven't been compressed or sized appropriately for how they're actually displayed.
Why HTML response time is checked separately from total weight
HTML response time measures how quickly your server itself responds, before the browser even starts downloading linked resources - a slow HTML response points to a server or hosting problem, while high total page weight points to too much content/assets being requested. Both affect load time, but the fixes for each are completely different.