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Kitty keyboard: REPORT_ALTERNATE (flag 4)
Flag 4 reports alternate key representations. When set, the terminal includes a shifted_key sub-parameter showing what key the user intended (e.g., Shift+1 reports both '1' and '!'). Without this flag, applications receive only the base key and must guess the shifted result based on keyboard layout — which varies by locale.
How this is tested: Push keyboard mode with flags 1+4 (
CSI > 5 u), query flags, verify bit 4 is set.Analysis2026-03-29
Supported by 9 of 13 terminals (69%). Not supported by: Terminal.app, Cursor, vt100.js, xterm.js. Part of the Rich TUI baseline. Notes: vt100.js: Not implemented — pure TypeScript emulator; xterm.js: Kitty keyboard protocol not implemented in xterm.js.
Supported by 9 of 18 backends (50%)
Terminal Applications
| Terminal | Version | Support | Notes |
|---|---|---|---|
| iTerm2 | 3.6.9 | ✓ yes | |
| cmux | ✓ yes | ||
| Ghostty | 1.3.1 | ✓ yes | |
| Kitty | 0.46.2 | ✓ yes | |
| VS Code | 1.113.0 | ✓ yes | |
| Warp | 0.2026.03.18.08.24.03 | ✓ yes | |
| Cursor | 2.6.21 | ✗ no | No kitty keyboard response |
| Terminal.app | 2.15 | ✗ no | No kitty keyboard response |
Headless Backends
Parser correctness only — a ✓ means the parser accepts the sequence.
| Backend | Version | Support | Notes |
|---|---|---|---|
| Alacritty | 0.26.0 | ✓ yes | |
| vterm | 0.2.0 | ✓ yes | |
| WezTerm | 0.1.0-fork.5 | ✓ yes | |
| vt100.js | 0.2.1 | ✗ no | Not implemented — pure TypeScript emulator |
| xterm.js | 5.5.0 | ? unknown | Kitty keyboard protocol not implemented in xterm.js |
| xterm.js | 6.0.0 | ? unknown | Kitty keyboard protocol not implemented in xterm.js |
| xterm.js | 5.4.0 | ? unknown | Kitty keyboard protocol not implemented in xterm.js |
| xterm.js | 6.1.0-beta.195 | ? unknown | Kitty keyboard protocol not implemented in xterm.js |