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DECALN screen alignment (ESC # 8)
ESC # 8DECALN (DEC Screen Alignment Test) fills the entire screen with the letter 'E'. The sequence is
ESC # 8. Originally designed for service technicians to verify screen alignment on CRT displays, it is now primarily used as a quick way to fill the screen with known content for testing purposes. DECALN also resets scroll margins and moves the cursor to the home position (row 1, column 1).How this is testedautomated
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\x1b#8 (DECALN), verify cell at (0,0) contains 'E'.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 10 of 14 backends (71%)
Terminal Applications
| Terminal | Version | Support | Notes |
|---|---|---|---|
| iTerm2 | 3.6.9 | ✓ yes | |
| Ghostty | 1.3.1 | ✓ yes | |
| VS Code | ✓ yes | ||
| Cursor | ✓ yes | ||
| Warp | ✗ no | ||
| Terminal.app | ✗ no |
Headless Backends
Parser correctness only — a ✓ means the parser accepts the sequence.
| Backend | Version | Support | Notes |
|---|---|---|---|
| Alacritty | 0.26.0 | ✓ yes | |
| Kitty | 0.40.0 | ✓ yes | |
| WezTerm | 0.1.0-fork.5 | ✓ yes | |
| xterm.js | 5.5.0 | ✓ yes | |
| vt100.js | 0.2.1 | ✗ no | DECALN not implemented in vt100.js baseline emulator |
| vterm | 0.2.0 | ✗ no | DECALN not implemented in vterm.js |