I Built a Privacy-First Calculator Website — Here is What I Learned About PageSpeed and SEO

I recently launched CalcFree (calcfree.online) — a
free calculator website with 25+ tools for health,
finance, and math.

Here are the results after launch:

Performance: 93/100
Accessibility: 94/100

Best Practices: 100/100
SEO: 100/100

Here is what helped achieve these scores:

1. Pure HTML/CSS/JS — No frameworks, no WordPress.
   Just clean semantic code. Loads in under 1 second.

2. All calculations run locally — No API calls, no
   server requests for calculations. JavaScript handles
   everything in the browser.

3. Proper semantic HTML — h1, h2, nav, main, footer
   elements used correctly. Helped both accessibility
   and SEO.

4. Meta tags from day one — title, description,
   og:tags, schema markup all set up before launch.

5. robots.txt and sitemap.xml — Submitted to Google
   Search Console and Bing Webmaster Tools on day one.

The site: https://calcfree.online

Has anyone else built pure HTML tools sites?
What was your experience with SEO?