Building Interactive Web Tools with Pure HTML/CSS/JS: Lessons from a Streaming Site

When we set out to build 7 interactive calculators for Optistream — a French streaming analytics site — we made a deliberate choice: no React, no Vue, no frameworks. Just pure HTML, CSS, and vanilla JavaScript, embedded directly into WordPress pages. Here's what we learned. Why No Framework? Our calculators needed to: Load instantly (no 200KB+ bundle) Work inside WordPress content areas Be maintainable by a small team Support LiteSpeed Cache without breaking A framework would have been overkill. These are single-purpose tools: input some numbers, get results. The DOM manipulation is minimal, the state is simple, and the logic is pure math. The 7 Calculators We Built We built tools for streamers to calculate their potential earnings, subscription revenue, and platform comparisons: Twitch Sub Calculator — Estimate earnings from subs at different tiers Twitch Revenue Calculator — Full revenue breakdown (subs, bits, ads, sponsors) Revenue comparison tool (Twitch vs Kick vs YouTube) Bits-to