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Cell size report (OSC 776)
ESC ] 776 BELOSC 776 reports the terminal's cell dimensions and font metrics. The query is
ESC ] 776 BEL and the terminal responds with the cell width, cell height, and font ascent/descent values in pixels — enabling applications to align Sixel or pixel-graphics output to the character grid. This was introduced in rxvt-unicode 9.29 and is essentially a urxvt-specific alternative to xterm's CSI 14 t (window pixel size) and OSC 1337 ReportCellSize (iTerm2). Like the other urxvt OSC extensions, it sees no adoption outside its origin terminal.How this is testedpartial
Send
Send
OSC 776 BEL and verify the terminal responds with cell metrics or silently consumes the query.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 all 4 tested terminals — universal adoption. Part of the Unicode baseline.
Supported by 6 of 14 backends (43%)
Terminal Applications
| Terminal | Version | Support | Notes |
|---|---|---|---|
| iTerm2 | 3.6.9 | ✓ yes | |
| Ghostty | 1.3.1 | ✓ yes | |
| Terminal.app | 2.15 | ✓ yes | |
| Kitty | 0.46.2 | ✓ yes | |
| VS Code | 1.113.0 | ? unknown | |
| Warp | 0.2026.03.18.08.24.03 | ? unknown | |
| Cursor | 2.6.21 | ? unknown |