Backend Capability Matrix

Each Termless backend wraps a different terminal emulator. They all implement the same TerminalBackend interface, but their underlying capabilities differ.

Capability Matrix

Capability	xterm.js	Ghostty	vt100	Alacritty	WezTerm	Peekaboo
Truecolor (24-bit)	Yes	Yes	Yes	Yes	Yes	Yes
Kitty keyboard	No	Yes	No	Yes	Yes	No
Kitty graphics	No	No	No	No	No	No
Sixel	No	No	No	No	Yes	No
OSC 8 hyperlinks	Yes	Yes	No	Yes	Yes	Yes
Semantic prompts	No	No	No	No	Yes	No
Unicode	15.1	15.1	15.1	15.1	15.1	15.1
Reflow on resize	Yes	Yes	No	Yes	Yes	Yes
Viewport scrolling	Yes	No	Yes	Yes	Yes	Yes
OS-level screenshot	No	No	No	No	No	Yes
Native deps	None	WASM	None	Rust (napi-rs)	Rust (napi-rs)	None
Build requirement	None	None	None	Rust toolchain	Rust toolchain	None

Backend Details

@termless/xtermjs

The default backend. Uses @xterm/headless — the same xterm.js terminal emulator used in VS Code's integrated terminal, but without a DOM renderer.

• Best for: Most testing scenarios. Well-tested, stable, zero native dependencies.
• Limitations: No Kitty keyboard protocol. Emoji width detection may differ from native terminals in headless mode.
• Install: Included automatically with @termless/test.

@termless/ghostty

Uses Ghostty's VT parser via ghostty-web WASM. Ghostty is a modern GPU-accelerated terminal with strong standards compliance.

• Best for: Testing against a modern, standards-compliant parser. Verifying Kitty keyboard protocol support.
• Limitations: WASM build does not support viewport scrolling or Kitty graphics. OSC title changes have no callback in WASM mode.
• Install: npm install -D @termless/ghostty

@termless/vt100

Pure TypeScript VT100 emulator with zero dependencies. Lightweight and fast, inspired by the Rust vt100 crate.

• Best for: Environments where you want zero native dependencies and zero WASM. CI runners with constrained environments.
• Limitations: No reflow on resize. No OSC 8 hyperlinks. No Kitty keyboard. More limited escape sequence coverage than xterm.js or Ghostty.
• Install: npm install -D @termless/vt100

@termless/alacritty

Uses Alacritty's alacritty_terminal crate via napi-rs native bindings. Alacritty is a GPU-accelerated terminal focused on simplicity and performance.

• Best for: Testing against Alacritty's VT parser. Cross-checking reflow behavior.
• Limitations: Requires Rust toolchain to build native bindings. Not available as prebuilt binaries yet.
• Install: npm install -D @termless/alacritty (requires Rust build)

@termless/wezterm

Uses WezTerm's wezterm-term VT parser via napi-rs native bindings. WezTerm has the broadest feature set of any terminal emulator.

• Best for: Testing sixel graphics support, semantic prompts, and the widest protocol coverage.
• Limitations: Requires Rust toolchain to build native bindings. Not available as prebuilt binaries yet.
• Install: npm install -D @termless/wezterm (requires Rust build)

@termless/peekaboo

OS-level terminal automation. Launches a real terminal application, sends keystrokes via OS accessibility APIs, and captures the terminal state via xterm.js data channel.

• Best for: End-to-end testing against a real terminal application (e.g., testing your app in actual Ghostty or iTerm2). OS-level screenshots of the real terminal window.
• Limitations: macOS only. Requires accessibility permissions. Much slower than in-memory backends. Not suitable for unit tests.
• Install: npm install -D @termless/peekaboo

Choosing a Backend

For most projects, the default xterm.js backend (included in @termless/test) is sufficient. Consider adding additional backends when:

• You ship a TUI that needs to work across different terminals
• You want to verify Kitty keyboard protocol handling (use Ghostty or Alacritty)
• You need sixel graphics testing (use WezTerm)
• You want the fastest possible zero-dep setup (use vt100)
• You need to test against a real terminal window (use Peekaboo)

See Multi-Backend Testing for how to configure Vitest to run tests against multiple backends.