External Protocols

Extensions to the VT vocabulary adopted from other terminals. These ride on the underlying byte stream but define their own structured payloads.

OSC-based

Most external protocols are layered on OSC because OSC supports arbitrary string payloads with a clean string-terminator.

Protocol	OSC	Origin	Otty	Doc
Hyperlinks	OSC 8	xterm / VTE	✓	OSC 8
Shell Integration	OSC 133	FinalTerm / iTerm2	✓	Shell Integration
Working Directory	OSC 7	VTE	✓	Files and Links
Notifications	OSC 9	iTerm2	✓	Notifications
Notifications (rich)	OSC 777	urxvt	✓	Notifications
Clipboard	OSC 52	xterm	✓ (opt-in)	Copy and Paste
Inline Image (iTerm)	OSC 1337	iTerm2	✓	Images

DCS / APC-based

Protocol	Introducer	Origin	Otty	Doc
Kitty graphics	APC (ESC _)	Kitty	✓ (mostly)	Images
Sixel graphics	DCS (ESC P)	DEC	☐ planned	—
tmux passthrough	DCS	tmux	◐	—

CSI-based

Protocol	Sequence	Origin	Otty
Kitty keyboard protocol	CSI > 1 u / CSI < u	Kitty	✓
Bracketed paste	CSI ?2004 h/l	xterm	✓
Focus reporting	CSI ?1004 h/l → CSI I / CSI O	xterm	✓
Synchronized output	CSI ?2026 h/l	iTerm2	✓ (buffered, with a safety timeout)
SGR mouse reporting	CSI ?1006 h/l	xterm	✓
Scroll-then-erase ED	CSI 22 J	Kitty	✓

Conformance notes

• OSC 133 follows the FinalTerm "FTCS" spec as adopted by iTerm2.
• Where iTerm2 and xterm differ on the same OSC number, Otty implements iTerm2's semantics (the more common modern target).

Identification

Sequence	Origin	Otty
CSI c — Primary DA	DEC	✓ (responds ?62;22c)
CSI > c — Secondary DA	DEC	✓
CSI > q — XTVERSION	xterm	✓ (replies DCS > | otty(<version>) ST)

See also

• Terminal Comparison — side-by-side support matrix vs xterm / iTerm2 / Kitty / WezTerm / Alacritty / Ghostty / foot.
• Sequence Reference — every sequence in one place.
• Shell Integration, Images, Notifications.