Introduction

WebNP2 is a web player that runs a WebAssembly build of the PC-98 emulator NP2kai in your browser. The goal is a "just open the URL" experience where you can resume right where you left off.

No ROM images or commercial software disk images are bundled. You load your own HDD/FD images by dragging and dropping them onto the screen.

Any disk image you load is saved only inside your browser (IndexedDB) and is never sent to any server.

Starting the emulator

A start overlay appears when you open the page. If no disk image is specified via URL, you get two choices: "Start As-Is" (start with no image loaded, then drag & drop one afterward) or "Start with FreeDOS(98)" (try it immediately with the bundled boot floppy). If a disk is specified via URL, a single "Click to Start" button is shown instead. If saved images exist in the library, a "Boot from Saved Disk" button also appears. Only these buttons start the emulator; clicking empty overlay space does nothing.

Due to browser autoplay restrictions, audio stays muted until you click (or, for auto-start, until your first click or key press).

Loading disk images

Dropping a file onto the screen area auto-detects whether it's an HDD or FD image based on its extension.

• HDD: .thd .hdi .nhd .hdd
• FD: follows the formats accepted by the NP2kai core itself (.bin is excluded to avoid false positives). .d88 .d98 .fdi .hdm .xdf .dup .2hd .nfd .fdd .hd4 .hd5 .hd9 .h01 .hdb .ddb .dd6 .dd9 .dcp .dcu .flp .tfd .fim .img .ima

There's an FDD1/FDD2/HDD slot row at the bottom of the player, with buttons for Insert, Insert FreeDOS(98) (FDD1 only), Eject, New Blank, and Download for each drive.

HDDs can only be handled before boot. The emulator core cannot swap a HDD while running, so the HDD slot buttons (Set, Set from library, Create blank HDD, Remove) are enabled only before boot. Dropping a HDD image before boot no longer starts the machine either: it is just set into the HDD slot (the slot name is shown in italics). Prepare its contents, then press the boot button.

Each slot row starts with an access lamp that glows red while that drive is being read or written, just like the drive LED on real hardware — a handy hint that the guest is touching the disk.

You can also open the page with URL parameters (?hdd=/?fd1=/?fd2=, etc.) to load images directly. See the URL parameters section of the README for details.

These parameters also accept a .zip / .lzh URL directly — if the fetched content is an archive, it's extracted automatically. A single disk inside is used right away; if it contains multiple disks, WebNP2 can't decide which one to boot, so it skips auto-start (even with run=1) and opens the Disk Library for you to choose.

?lib=URL (repeatable, e.g. &lib=URL2) is a sharing-link parameter that only registers images in the Disk Library, regardless of kind (FD/HDD). It never auto-inserts into a slot — the Library always opens — and skips run=1 auto-boot whenever it's given.

File transfer (browser ⇔ disk image)

More (…) → Disk → File Transfer opens an FTP-client-style two-pane dialog. The top/left pane is "This browser" and the bottom/right pane is "Disk image (PC-98 side)".

• "This browser" accepts files via a file picker or drag-and-drop. .lzh / .zip archives are automatically extracted, and their contents are listed directly.
• "Disk image (PC-98 side)" lets you pick a target (a running FDD1/FDD2, or an FD image from the library), then browse the file list, navigate directories, delete files, and create new folders. Free space is also shown.
• The "Create Transfer FD" button creates a formatted 1.2MB FD image with one click and saves it to the Disk Library.
• Use the center arrow buttons (→/←, or ↓/↑ on narrow screens) to transfer files. Long filenames are shortened to 8.3 format, with a confirmation before writing.

Transfers to a running FDD are safe even while the emulator is running: after writing, the drive is automatically ejected and reinserted so the guest DOS recognizes it as a media swap. However, avoid transferring while the guest is actively accessing the floppy (FDD light on). The .d88 format is not supported for editing. HDD images (.thd .nhd .hdi .hdd) can only be selected before boot — the emulator core cannot swap a HDD while running, so they disappear from the list once the machine has started.

A typical use case: drop a PC-98 freeware archive (.lzh) onto the browser side, write it to a transfer FD, then run it from the guest's DOS. The reverse direction (guest → browser, i.e. downloading) also works.

Toolbar and More menu

Pause, Fullscreen, On-screen Keyboard, Screenshot, and More (…) stay centered, while Reset Machine is split off to the right end. It's kept a finger's width away from the buttons you press often, because a stray tap would wipe out whatever state is currently running. More contains Display, Input, Sound, Disk, and State groups plus direct rows for ROM Files, Debugger, Help, and Language. Language shows a globe and the current value. Display is the screen aspect mode (defaults to 4:3, matching a real CRT; can be switched to pixel-perfect).

Pausing lowers host CPU load (measured: about 62% while running → settles to 1–3% within a few seconds after pausing). Simply switching to another tab does not lower it — browsers don't throttle a tab that's playing audio.

Using on a smartphone

On screens narrower than 640px, the display is automatically scaled down by a fractional factor so it never overflows.

Touch input maps onto mouse operations. A tap is a left click, dragging your finger moves the cursor, and holding still for about 0.5 seconds (long press) before moving performs a left-button drag. A two-finger tap is a right click.

The keyboard icon in the toolbar opens/closes a PC-98 layout on-screen keyboard. SHIFT/CTRL/GRPH are one-shot modifiers that apply to only the next keystroke (shown lit while active), while CAPS/Kana are lock toggles. The numeric keypad block is hidden by default; toggle it with the “Tenkey” key inside the keyboard panel.

Just like the real hardware, holding a key down triggers key repeat after a short delay (this also applies to a physical keyboard).

More (…) → Input → Input Settings has three tabs: Gamepad, Keyboard, and Virtual Pad. Map physical gamepad buttons/axes or host keys to PC-98 keys using the shared PC-98 keyboard picker. Host-key remapping is off by default and includes a built-in “Tenkey Movement (Arrows → Tenkey)” profile that you can duplicate and edit.

In portrait, the Virtual Pad appears below the screen; in landscape, it uses the left and right margins. The dark page background keeps its light controls visible. When space is tight in landscape, each drive name remains visible while its FDD/HDD action buttons wrap onto extra rows. A ⌨ / 🎮 / 🖱 switch appears immediately after the keyboard button whenever any one of the on-screen keyboard, Virtual Pad, or Virtual Trackpad is visible. Press 🎮 again while the pad is active to choose a profile or edit assignments. While any input panel is open, the layout shrinks to fit one screen, which temporarily hides the floppy slot row (close the panel before swapping disks).

Tapping 🖱 opens the Virtual Trackpad strip. A one-finger drag moves the cursor relatively, a short tap is a left click, a two-finger tap is a right click, and a press-and-hold for about 450ms then drag performs a left-button drag. The classic absolute-tracking touch on the emulator canvas itself still works alongside it. The usual trackpad gesture for scrolling (a two-finger drag) is not supported, since the PC-98 bus mouse only has two buttons and nothing on the guest side would receive it.

Sending text (typing Japanese)

Choose More (…) → Input → Send Text, or press Shift twice in a row (within 0.5 seconds, no other key in between) to open the send-text bar.

Text you type on the host (this page) is sent to the guest (inside the emulator) as keyboard input. Check "With Enter" to append a newline at the end.

Full-width characters (Shift_JIS) reach the guest directly on environments that support them, such as FreeDOS(98). On a plain NEC MS-DOS console, full-width characters may come out garbled. In that case, click the "Enable full-width input" button inside the text send bar. It installs a resident helper (PASTE.COM) from the bundled tool floppy into the guest, after which full-width text can be sent. Run it while DOS is sitting at a command prompt.

Saving and resuming

Use More (…) → State → Save State / Load State to snapshot and restore the running state to/from a slot.

Disk changes are also auto-saved to your browser (IndexedDB), so opening the same image again resumes from where you left off. The Disk Library lets you boot, insert into an FD drive, rename, or delete any previously saved HDD/FD image.

Dropping a .zip / .lzh archive extracts just the disk images inside and adds them to the library. A single disk boots right away; multiple disks are grouped into a folder and the library opens so you can pick one. Click a folder row to expand it. Dropping a disk image or .zip / .lzh archive onto the Disk Library dialog itself only registers it in the library, without setting it into any slot.

If you don't have a HDD image, the "Create blank HDD" button on the HDD slot builds an empty FAT16-formatted 40MB disk on the spot. It is saved to the library and set into the HDD slot right away. It carries no IPL (boot code), so it cannot boot on its own — boot DOS from a floppy and use it as a data drive (FreeDOS(98) picks it up as C:).

You can also swap disks from the "Insert from library" button on each FD slot. Selecting a folder switches the menu to the disks it contains, so you can move to disk 2 or 3 without opening the library. "Rename" changes the displayed name only; the original file name is kept.

"Reset to Original" discards your saved progress and restores the originally distributed image (a confirmation dialog appears first).

It is saved inside your browser (and when that disappears)

Autosave writes to your browser's storage (IndexedDB), not to a server. It behaves just like cookies, and it all disappears when:

• You clear "Cookies and other site data" (clearing only "Cached images and files" does not remove it)
• You clear browsing data with site data included
• You close a private/incognito window
• The device runs low on space and the browser reclaims storage
• You don't open this site in Safari for seven days (WebKit deletes all script-writable storage)

Registering ROM/asset files

If you have ROM/asset files used by the desktop version of NP2kai (bios.rom, itf.rom, sound.rom, font.rom, 2608_*.wav, etc.), you can register them via More (…) → ROM Files. Files are saved only in your browser (IndexedDB) and automatically loaded on future starts. Nothing is sent to any server. Reload the page for changes to take effect.

Rhythm sounds (2608_*.wav) already come with substitute samples bundled in, so the rhythm part plays even if you never register anything. Those bundled sounds are not the real YM2608 rhythm samples, though — they are a substitute. If you register genuine 2608_*.wav files dumped from real hardware, those take priority instead. Only mono, linear PCM, 16-bit WAV files can be registered; files that don't meet this will be rejected with a reason shown, rather than registered (this prevents all six samples from going silent together).

Controlling WebNP2 from AI agents (MCP)

WebNP2 can be driven by AI agents such as Claude Code through a local MCP server (webnp2-mcp). The MCP server always runs on your own machine, and screen contents or disk images are never sent to any external server.

Open WebNP2 with the ?bridge=1 parameter to have the page connect to your local MCP server. Some of the main tools:

See mcp/README.md for full setup instructions.

Troubleshooting

• No sound — Due to browser restrictions, audio stays muted until your first click (or, for auto-start, until your first click/key press).
• Fetching a URL-specified image fails — URLs given via hdd/fd1/fd2 must be served from an origin with CORS (Access-Control-Allow-Origin) enabled. Dropbox share links can be pasted exactly as "Copy link" gives them to you (no need to change dl=0 to dl=1: the app rewrites the hostname to dl.dropboxusercontent.com and fetches directly, falling back to the relay if that fails). Google Drive is automatically retried through a relay service. OneDrive share links can't be used.
• The mouse cursor drifts — Use More (…) → Input → Resync Mouse to re-establish the reference point.
• Full-width characters come out garbled — See the "Sending text (typing Japanese)" section above. Installing the guest helper via "Enable full-width input" fixes this.