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OSC 133;A prompt start (FTCS_PROMPT)
ESC ] 133 ; A BELOSC 133;A (also known as FTCS_PROMPT) marks the start of a shell prompt — the first of the FinalTerm semantic prompt markers. It tells the terminal: everything from here until the next marker is the prompt itself. Shells emit this immediately before drawing the prompt string.
This marker enables click-to-navigate between prompts, jump-to-previous-command, and visual command boundaries. Without it, the terminal has no way to know where one command ends and the next begins — it just sees a stream of characters. Combined with 133;B, 133;C, and 133;D, it forms the complete FinalTerm semantic prompt protocol.
How this is testedautomated
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OSC 133 ; A BEL and verify the terminal consumes the sequence (cursor doesn't advance, terminal remains responsive).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 9 tested terminals — universal adoption. Part of the Rich TUI baseline.
Supported by 13 of 14 backends (93%)
Terminal Applications
| Terminal | Version | Support | Notes |
|---|---|---|---|
| iTerm2 | 3.6.9 | ✓ yes | |
| Ghostty | 1.3.1 | ✓ yes | |
| VS Code | ✓ yes | ||
| Warp | ✓ yes | ||
| Cursor | ✓ yes | ||
| Terminal.app | ✓ yes |