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Report window title (CSI 21 t)
ESC [ 21 tXTWINOPS subcode 21 queries the current window title. The query is
CSI 21 t; the response is OSC l title ST. Applications use this to save the current title before overwriting it (so they can restore it on exit) — historically the only reliable way before XTPUSH/POP TITLE (CSI 22/23 t) was added.
Many modern terminals refuse to report window titles by default for security reasons. A hostile escape sequence injected into the terminal could otherwise read a title set by a different application and exfiltrate it. xterm controls this via the allowWindowOps resource. Applications that need title save/restore should prefer the title stack (CSI 22/23 t) which works without exposing the title to other processes.How this is testedpartial
Send
Send
\x1b[21t, verify the terminal sends an OSC l response. Many real terminals refuse to report titles for security; headless emulators that don't store titles return partial.The same probe runs against headless backends (via Termless) and real terminal apps (via a daemon launched in each terminal). This lets us distinguish parser correctness from rendering correctness.
Analysis2026-04-06
Supported by 3 of 9 terminals (33%). Part of the Rich TUI baseline.
Supported by 1 of 14 backends (7%)
Terminal Applications
| Terminal | Version | Support | Notes |
|---|---|---|---|
| iTerm2 | 3.6.9 | ✓ yes | title: bun |
| Ghostty | 1.3.1 | ✗ no | No XTWINOPS 21 response (terminal may refuse for security) |
| Terminal.app | 2.15 | ✗ no | No XTWINOPS 21 response (terminal may refuse for security) |
| Kitty | 0.46.2 | ✗ no | Window operations not exposed via Python batch bridge |
| VS Code | 1.113.0 | ? unknown | |
| Warp | 0.2026.03.18.08.24.03 | ? unknown | |
| Cursor | 2.6.21 | ? unknown |
Headless Backends
Parser correctness only — a ✓ means the parser accepts the sequence.
| Backend | Version | Support | Notes |
|---|---|---|---|
| WezTerm | 0.1.0-fork.5 | ~ partial | Window title report requires a real window system |
| xterm.js | 5.5.0 | ~ partial | Window title report not exposed in xterm.js headless mode |
| Alacritty | 0.26.0 | ✗ no | Window title report not implemented by alacritty |
| vt100.js | 0.2.1 | ✗ no | XTWINOPS not implemented — post-dates VT220 baseline |
| vterm | 0.2.0 | ✗ no | XTWINOPS window title report not implemented in vterm.js |