The game uses WebGL, a faster way to render graphics on a computer but this also means that it can take a lot of power to run the game. If you’re playing slither.io on a laptop and you’re experiencing lag, the first thing to do is check if your graphics card is up to scratch.
Closing unnecessary/extra tabs.
Closing unnecessary/extra windows.
Turning off any videos or music in the background if need be.
Restarting your Internet router.
Turning off Wifi, waiting a few minutes, and then re-enabling Wifi.