Download a dedicated emulator and supply your own ROM (preferably dumped from a cartridge you own):

One reliable option is the dedicated Pokémon gaming portal at pokemongames.games. This site runs Pokémon Ruby using HTML5 technology, delivering smooth performance across all devices without requiring downloads or installations. The game loads directly in your browser after a short advertisement and supports standard GBA emulator controls:

While the convenience is undeniable, playing Pokémon Ruby on unblocked gaming sites comes with caveats that players should be aware of.

If the audio crackles or the game stutters, your browser may be throttling the tab's performance. Turn off hardware acceleration in your browser settings, close competing background tabs, or toggle the emulator’s frameskip feature to achieve a smooth 60 frames per second. Getting Started in Hoenn: Strategy Guide