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Tertiary Device Attributes (DA3)
ESC [ = cDA3 (CSI = c) returns the terminal's unit ID as a DCS response. Less commonly supported than DA1/DA2, primarily by xterm and terminals that aim for high VT compatibility.
How this is testedautomated
Send CSI = c, check for a DCS ! | response.
Send CSI = c, check for a DCS ! | response.
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 14 backends (21%)
Terminal Applications
| Terminal | Version | Support | Notes |
|---|---|---|---|
| iTerm2 | 3.6.9 | ✓ yes | |
| Ghostty | 1.3.1 | ✗ no | No DA3 response |
| VS Code | ✗ no | ||
| Warp | ✗ no | ||
| Cursor | ✗ no | ||
| Terminal.app | ✗ no |
Headless Backends
Parser correctness only — a ✓ means the parser accepts the sequence.
| Backend | Version | Support | Notes |
|---|---|---|---|
| vterm | 0.2.0 | ✓ yes | |
| Alacritty | 0.26.0 | ~ partial | Headless mode has no output stream for DA3 responses |
| Kitty | 0.40.0 | ~ partial | Headless mode has no output stream for DA3 responses |
| WezTerm | 0.1.0-fork.5 | ~ partial | Headless mode has no output stream for DA3 responses |
| vt100.js | 0.2.1 | ✗ no | No output stream — pure TypeScript emulator |
| xterm.js | 5.5.0 | ✗ no | DA3 not implemented in xterm.js |