600 Snakes on the Edge: How I Built a Slither.io Server with Trail Algorithms, Spatial Hashing & Bot AI

I spent one week building a multiplayer Slither.io clone. The server runs on PartyKit + TypeScript, the client on Phaser 3 + React. Honestly the code is far from perfect — there are hard-coded magic numbers, TODO comments, and parts I would definitely refactor if I had more time — but it works. One room supports 600 snakes (100 real players + 500 bots) and the latency feels fine. This post is about the core algorithms and the bugs I stepped on. 1. Why PartyKit? I initially wanted to write the se