The same checks the SEO Optimizer runs inside Tootela, on one page at a time instead of your whole site.
Title and description length, canonical, robots, Open Graph and Twitter cards, viewport, language, favicon.
One H1 or many, heading hierarchy, word count, text-to-HTML ratio, internal and external links, generic anchors.
HTTPS, structured data and its types, sitemap, robots.txt, hreflang, render-blocking scripts, load time.
Images without alt text, missing viewport, missing language, heading order.