SEO Check by altitude-dev.com is a free Chrome extension that allows you to analyze the webpage you are currently visiting and obtain valuable information about your website's SEO and potential optimizations. With this extension, you can gain insights into your site's technical issues, language, CMS detection, and more.

In terms of SEO, the extension provides a comprehensive analysis, including the page's title, meta description, URL friendliness, keywords, semantic structure, image optimization, alt attributes, mixed content, sitemap, robots.txt, social media presence, external and internal links, page speed, DOM size, inline CSS, deferred JavaScript, deprecated HTML, meta viewport, page compression, size, and CSS/JS/MEDIA requests.

Additionally, SEO Check offers enriched features such as Canonical tags, OpenGraph tags, and Twitter Graph/Card.

The extension also focuses on security by checking for SSL/HTTPS, email exposure, protection against XSS attacks, iframes, MIME types, and the Referrer-Policy header. It also provides information about the technology used.

For environmentally conscious website owners, SEO Check includes an ecological feature that detects the usage of a green web hosting server and estimates the CO2 emissions per visitor based on the page's weight.

Furthermore, the extension offers a Whois Domain feature that provides information about the registrar, owner, location, domain details (creation, expiration, update), Whois server, SSL organization, issuer, signature, expiration, server IP, and various DNS records (A, AAAA, MX, NS, TXT).

Please note that this extension is currently in its alpha version.