OSC 133 — Semantic Prompts (FinalTerm / FTCS shell integration)

OSC 133 marks shell prompt, command-input, and command-output boundaries so terminals can navigate by command, fold output, and color the prompt by exit status. Four subcommands: A (prompt start), B (command-line start), C (output start), D[;exitcode] (command finished). Originated in the defunct FinalTerm emulator; harmonized by Per Bothner's Semantic Prompts proposal; near-universally adopted.

aka: FTCS · FinalTerm prompt markers · FinalTerm sequences · semantic prompts · shell integration marks · FTCS_PROMPT/FTCS_COMMAND_START/FTCS_COMMAND_EXECUTED/FTCS_COMMAND_FINISHED

parameters / subcommands

id	name	bytes (ST)	meaning
A	FTCS_PROMPT	\x1b]133;A\x1b\	Start of the prompt. Emitted by the shell precmd hook just before printing PS1.
B	FTCS_COMMAND_START	\x1b]133;B\x1b\	Start of the command line / end of the prompt. Everything after this until C is what the user typed.
C	FTCS_COMMAND_EXECUTED	\x1b]133;C\x1b\	Start of command output / end of the command line. Emitted from the shell preexec hook, just before the command runs.
D	FTCS_COMMAND_FINISHED	\x1b]133;D\x1b\	End of the command. Optional exit code as a second parameter: 0 = success, nonzero = error. Omitting the exit code leaves the mark default-colored (no success/error tint).

support matrix

terminal	level	since	notes
FinalTerm	full	original (defunct)	Origin of the FTCS sequences; project is defunct but documented by iTerm2.
iTerm2	full	Shell Integration (3.x)	Documents the sequences; also defines its own OSC 1337 family for additional shell-integration features.
VTE / GNOME Terminal	full	VTE 0.66+	Recognizes OSC 133 A/B/C/D for prompt/command tracking.
WezTerm	full	documented	Implements semantic zones from OSC 133; documents shell integration.
kitty	full	documented	Uses OSC 133 for shell integration / command tracking.
Ghostty	full	1.0	Supports OSC 133 shell integration out of the box.
Windows Terminal	full	stable shell-integration tutorial	Documents A/B/C/D identically to Contour; supports D exit-code coloring.
Contour	full	documented	Dedicated OSC-133 shell-integration page; authoritative cross-source for A/B/C/D.
VS Code integrated terminal	variant	shell integration	Prefers OSC 633 (superset) but also accepts/emits OSC 133 for portability.
Warp	partial	documented	Block model derives from prompt/command boundaries; uses shell-integration marks though its native model predates a pure 133 dependency.
DomTerm	full	Per Bothner ref impl	Reference implementation behind the Semantic Prompts proposal.

variants

OSC 633 (VS Code) — terminal-osc/633 VS Code's integrated terminal uses OSC 633 as a superset/sibling of OSC 133 (633;A/B/C/D mirror 133, plus 633;E command line, 633;P properties like Cwd). VS Code emits BOTH 133 and 633 for portability. Treat 633 as a distinct entry; cross-linked via see_also.
FTCS_COMMAND (P;) — terminal-osc/133 Some implementations add OSC 133 ; P ; key=value ST for aux properties (e.g. Cwd, prompt kind) and OSC 133 ; L for fresh-line. These are extensions in the Semantic Prompts proposal beyond the core A/B/C/D and support varies; treat as partial.

gotchas

Terminator divergence: ECMA-48 requires ST (ESC \, i.e. \x1b\x5c). xterm and nearly every modern terminal ALSO accept BEL (\x07). Emit ST; accept both when parsing. Mixing a bare ESC followed by an unrelated byte will mis-terminate the string.
Wrap marks in PROMPT_COMMAND/precmd, not inside the visible PS1 width calculation: in bash/zsh the mark bytes must be wrapped in \[ \] (bash) or %{ %} (zsh) so the shell does not count them as visible columns, otherwise line editing and wrapping break.
C must be emitted from preexec (just before the command runs), not from precmd, or output folding will include the command line itself.
D's exit code is OPTIONAL; if you always want success/error coloring you must pass it explicitly (\x1b]133;D;$?\x1b\). A bare D leaves the mark untinted.
OSC 633 (VS Code) is NOT the same entry: 633 is a superset with extra subcommands (E command-line, P properties). Do not assume a 133 parser handles 633;P key=value.
There is NO registry for the number 133 itself; collisions are possible in principle but 133 is de-facto reserved for FinalTerm/FTCS across the ecosystem.
8-bit forms (0x9D for OSC, 0x9C for ST) exist per ECMA-48 but are rarely used in UTF-8 locales because they collide with UTF-8 continuation bytes; always prefer the 7-bit ESC-based forms in modern pipelines.

provenance

source: https://gitlab.freedesktop.org/Per_Bothner/specifications/-/blob/master/proposals/semantic-prompts.md
version: semantic-prompts.md @ gitlab.freedesktop.org/Per_Bothner/specifications master (unversioned living document)
retrieved: 2026-05-29 · updated: 2026-05-29T00:00:00Z

per-fact attribution:

#summary — https://gitlab.freedesktop.org/Per_Bothner/specifications/-/blob/master/proposals/semantic-prompts.md Semantic Prompts proposal is the harmonizing cross-terminal spec; defines purpose of prompt/input/output marking.
#A — https://learn.microsoft.com/en-us/windows/terminal/tutorials/shell-integration OSC 133 ; A ST = FTCS_PROMPT, start of prompt. Stated identically by Windows Terminal docs and Contour.
#A — https://contour-terminal.org/vt-extensions/osc-133-shell-integration/ Second independent source for A semantics (quorum).
#B — https://learn.microsoft.com/en-us/windows/terminal/tutorials/shell-integration OSC 133 ; B ST = FTCS_COMMAND_START, start of command line / end of prompt.
#B — https://contour-terminal.org/vt-extensions/osc-133-shell-integration/ Second independent source for B semantics (quorum).
#C — https://learn.microsoft.com/en-us/windows/terminal/tutorials/shell-integration OSC 133 ; C ST = FTCS_COMMAND_EXECUTED, start of command output / end of command line.
#C — https://contour-terminal.org/vt-extensions/osc-133-shell-integration/ Second independent source for C semantics (quorum).
#D — https://learn.microsoft.com/en-us/windows/terminal/tutorials/shell-integration OSC 133 ; D [ ; exitcode ] ST = FTCS_COMMAND_FINISHED; 0 success, nonzero error; omitting exitcode leaves the mark default-colored.
#D — https://contour-terminal.org/vt-extensions/osc-133-shell-integration/ Second independent source for D semantics including optional exit code (quorum).
#origin — https://iterm2.com/documentation-escape-codes.html iTerm2 states the sequences were pioneered by the now-defunct FinalTerm emulator and documents them.
ext.terminator — https://invisible-island.net/xterm/ctlseqs/ctlseqs.html OSC frame is ESC ] ... terminated by ST (ESC \\); xterm convention also accepts BEL (0x07) as terminator.
ext.frame — https://invisible-island.net/xterm/ctlseqs/ctlseqs.html OSC = ESC ] (0x9D in 8-bit). ECMA-48 5th ed. 1991 defines the OSC frame and ST; command numbers are not registered anywhere.

agent: curl -H 'accept: application/json' wire.phall.io/terminal-osc/133 or /terminal-osc/133.json