Fix Stutter and Lag In HTML5 Games

Your first step should be to clear the tab stack. Open tabs consume resources and can "fight" for the CPU with your game. Especially if you have other games or embedded ads or videos in other tabs. It's best to close unnecessary tabs, especially those with games or streaming services, before opening a new window or re-opening a game.

Games are sometimes embedded within a thicc surrounding site. If you have an option to make the game fullscreen and bypass the extra chrome, it'll likely reduce the amount of pixels that need to be refreshed each frame.

Make sure that your browser's setting for hardware acceleration is turned on. It allows your modern browser to offload some of the canvas and WebGL processing onto your GPU. You might have to restart your browser for it to take effect.

Some extensions inject their CSS/JS into all webpages, including your game. Ad blockers are generally good and safe extensions, but some privacy tools might break things in a game, especially if they modify WebSockets or XML/JSON traffic.

Modern games have a slider that reduces the graphical fidelity. On a PC, this can involve reducing particle effects, the quality of shadows or the resolution scale. On mobile, the issue can often occur if the phone begins throttling performance to cool down the device.

To fix it, try to not play on a consistently hot device, or play in short bursts (especially on phones). Using a desk fan while playing a graphics intensive game can go a long way.

Make sure you aren't low on memory (RAM). Having too many apps opened at once will put strain on your system, especially if you're on a mobile device. Particles and post-processing effects are usually more taxing than directional audio. It's better to reduce graphical effects before lowering the quality of your sounds.