Cross-Backend Conformance

termless verifies that all backends (xterm.js, Ghostty, vt100) produce identical results for the same VT100/ECMA-48 input sequences. Differences between backends are bugs — this is how we find and fix them.

Test Coverage

The cross-backend.test.ts suite runs 120+ tests across all backends, covering:

Category	What's tested
Text rendering	Plain text, multiline, CUP positioning, line wrap at boundary
Cell styles (SGR)	Bold, italic, faint, strikethrough, inverse, underline, truecolor FG/BG, 256-color, combined styles, SGR reset
Cursor	Position after text, after CRLF, CUP, CUF forward
Modes	Alt screen toggle, bracketed paste, auto wrap, application cursor, mouse tracking, focus tracking
Wide characters	Emoji width, CJK characters, column offset after wide chars
Scrollback	Screen lines reported, scrollback accumulation
Reset	reset() method, RIS (\ec) escape sequence
Capabilities	Truecolor, reflow, Kitty keyboard
Key encoding	Enter, Escape, Ctrl+C, ArrowUp
Cross-backend comparison	Cell-by-cell text, cursor position, and style attribute comparison between xterm.js and Ghostty

Running

bun vitest run vendor/termless/tests/cross-backend.test.ts --project vendor

Known Differences

• Emoji width: xterm.js headless does not report emoji as wide (CJK works correctly)
• Kitty keyboard: Ghostty supports it, xterm.js and vt100 do not
• OSC title: Ghostty WASM has no title change callback; vt100 backend has limited OSC support