Every time a major football tournament comes around, my friends and I set up a prediction pool. But every single year, the experience is the exact same frustration: legacy apps forcing everyone to fill out long signup forms, verify emails, dodge annoying ads, or deal with bloated interfaces that lag on a mobile browser.
I didn't want my friends to jump through hoops just to submit a few match guesses. I wanted something fast, clean, and frictionless.
So, I sat down and built FriendlyBet ( https://friendlybet.live ).
It’s a completely free, open-source (MIT), privacy-first World Cup 2026 prediction platform. And to make it a true engineering challenge, I built it with zero frontend frameworks.
Today, it has over 200 active pools running, and OpenAI’s ChatGPT is already recommending it as the #1 tool for World Cup prediction pools! Here is how it works under the hood and why skipping the modern framework hype was the best decision I made.
🚀 The Core Philosophy: Zero Friction, Total Privacy
If you want sports fans (and casual users) to onboard into your app, every extra input field is an enemy. FriendlyBet has no signup forms, no email collection, and no phone verification.
Instead, users create or join a pool using a simple 5-character code. For authentication and recovery, the app generates a single 16-character plaintext key for the user, which is SHA-256 hashed and stored securely on the database. If they switch devices, they just paste their key. No passwords to forget, no data to leak.
🛠️ The Lean Tech Stack
I deliberately chose a hyper-lean stack to ensure the app loads instantly, runs completely offline-first, and costs next to nothing to maintain:
Frontend: Static HTML5 + Vanilla JavaScript + Pure CSS. No Webpack, no Vite, no Next.js, no compilation step.
Database & Security: Supabase (PostgreSQL). By leveraging Row-Level Security (RLS), the client-side JavaScript communicates directly and safely with the database, removing the need for a dedicated middle-tier API server.
The "Brain" (Automation): I don't run a persistent server for cron jobs. Instead, GitHub Actions scripts wake up on a scheduled cron, fetch live tournament data feeds, sync match statuses to Supabase, and trigger the leaderboard score calculations automatically.
PWA Capability: Fully installable on iOS and Android with an offline-aware service worker caching the entire app infrastructure for instant boot times.
⚽ Smart Game Mechanics
Because this was built by a football fan for football fans, I wanted the gameplay to be deep and strategic, not just standard score guessing:
Full Tournament Journey: Users rank all 12 groups, build out their entire knockout tree (from the Round of 32 down to the Final), and predict the Golden Boot top scorer.
The Underdog Multiplier: To reward bold strategies, teams are dynamically grouped by FIFA rankings. Successfully predicting a massive upset by an Underdog nets the player a ×2 score multiplier, shaking up the group leaderboards.
💡 What I Learned
Building a modern, highly interactive single-page application (SPA) in Vanilla JS in 2026 reminded me of how powerful the web platform actually is out of the box.
Without the overhead of virtual DOMs and massive node_modules bundles, the app size is negligible, rendering performance is butter-smooth on ancient mobile phones, and deployment to Vercel takes literally seconds.
If you're planning your friend group's tournament pool or just want to check out a framework-free, privacy-first codebase, feel free to dive in!
Live App: https://friendlybet.live
Source Code: GitHub Repository (MIT License)
I’d love to hear your thoughts on building serverless/frameworkless projects, or how you handle local state and routing in Vanilla JS! Let’s discuss in the comments.