WebMSX is a complete MSX emulator written in JavaScript by Paulo Augusto Peccin. It runs entirely in your browser and supports MSX1, MSX2, MSX2+, and MSX turbo R machines. It uses the open-source C-BIOS firmware, so no copyrighted BIOS files are required.

The packer supports the most common MSX file formats:

• .rom / .mx1 — ROM cartridge images (loaded as Cartridge 1)
• .mx2 — MX2 cartridge images (loaded as Cartridge 1, defaults to MSX2)
• .dsk — Floppy disk images (loaded in Disk A)
• .cas — Cassette tape images (loaded as Tape, defaults to MSX1)
• .zip — ZIP archives (auto-detected by WebMSX)

Yes! All processing happens entirely in your browser. No files are uploaded to any server. The only network request is to download the WebMSX engine (from the local mirror or the GitHub CDN). The generated HTML file is 100% self-contained and works completely offline.

The generated HTML file embeds the WebMSX emulator engine and your game data (base64-encoded) into a single HTML file. When you open it in a browser, WebMSX boots the MSX machine and automatically loads your game. No internet connection is needed — it's fully self-contained.

• WebMSX — by Paulo Augusto Peccin (webmsx.org)
• C-BIOS — Open source MSX BIOS by the C-BIOS team
• Portable Retro Games — Open-source project (GitHub)