I Built a YouTube Watch-Together Extension in a Day

TL;DR: My friend and I wanted to watch YouTube together from different cities. Every existing solution required a separate website or screen sharing. So I built a Chrome extension that syncs playback with a toggle. Supabase Realtime, zero backend, one afternoon, under 1,200 lines of TypeScript. You and a friend are in different cities. You want to watch the same YouTube video at the same time. Pause when they pause, seek when they seek, switch videos together. There are services for this, but they all require opening a separate website, pasting links, or screen-sharing through a call. What if you just... toggled a switch next to your friend's name, and your browsers synced? That is what YPlay does. A Chrome extension backed by Supabase Realtime, built entirely in one sitting. Under 1,200 lines of TypeScript, one external dependency beyond React, and zero backend infrastructure beyond a free Supabase project. The Problem With "Just Watch Together" Every watch-together tool I tried had t