wterm

A terminal emulator for the web.

wterm ("dub-term") renders to the DOM — native text selection, copy/paste, find, and accessibility come for free. The core is written in Zig and compiled to WASM for near-native performance.

• Pluggable cores — built-in lightweight Zig core (~12 KB) or opt-in libghostty backend (~400 KB) for full VT compliance
• Zig + WASM core — VT100/VT220/xterm escape sequence parser compiled to a ~12 KB .wasm binary (release build)
• DOM rendering — native text selection, clipboard, browser find, and screen reader support
• Dirty-row tracking — only touched rows are re-rendered each frame via requestAnimationFrame
• Themes — CSS custom properties with built-in Default, Solarized Dark, Monokai, and Light themes
• Alternate screen buffer — vim, less, htop, and similar apps work correctly
• Scrollback history — configurable ring buffer
• Wide Unicode cells — CJK, fullwidth, and emoji codepoints keep cursor-addressed redraws aligned
• 24-bit color — full RGB SGR support
• Auto-resize — ResizeObserver-based terminal resizing
• WebSocket transport — connect to a PTY backend with binary framing and reconnection

• Zig 0.16.0+
• Node.js 24+
• pnpm 11+

pnpm install

zig build

For a release build:

zig build -Doptimize=ReleaseSmall

The built binary is committed at packages/@wterm/core/wasm/wterm.wasm and CI fails if it does not match the Zig sources, so rebuild and commit it with any change under src/.

src/unicode_width_table.zig holds the East Asian Width ranges the core uses to decide cell width. It is generated, not hand-edited. Run this when Unicode publishes a new version, after bumping UNICODE_VERSION in the script:

node scripts/gen-unicode-width.mjs

pnpm build

Serve the web/ directory with any static file server:

cd web && python3 -m http.server 8000

All dev servers use portless to avoid hardcoded ports. Each app is served at a .localhost URL (e.g. nextjs-example.wterm.localhost).

cp web/wterm.wasm examples/nextjs/public/
pnpm --filter nextjs dev

zig build test

Apache-2.0