{
  "id": "terminal-osc/50",
  "family": "terminal-osc",
  "slug": "50",
  "title": "OSC 50 — Set font",
  "summary": "OSC 50 ; spec ST sets the terminal font at runtime. In xterm the spec is an X Logical Font Description (or '#N' to pick a numbered font from the menu); a bare '?' or empty query asks the current font back. iTerm2 also implements OSC 50 to change the session font. It is a de-facto, divergent feature across the two.",
  "kind": "control-sequence",
  "aliases": [
    "set font",
    "OSC 50",
    "ESC ] 50",
    "change font"
  ],
  "status": "de-facto",
  "verification": "verified",
  "tier": "C",
  "source_url": "https://invisible-island.net/xterm/ctlseqs/ctlseqs.html",
  "source_version": "xterm ctlseqs, patch #410, 2026/04/19",
  "retrieved_date": "2026-05-29",
  "attribution": [
    {
      "claim_ref": "#xterm",
      "source_url": "https://invisible-island.net/xterm/ctlseqs/ctlseqs.html",
      "source_version": "xterm patch #410, 2026/04/19",
      "note": "xterm ctlseqs: Ps = 5 0 -> Set/query font. Pt is a font name (XLFD) or '#N' to select font N from the configured list; a query reports the current font."
    },
    {
      "claim_ref": "#iterm2",
      "source_url": "https://iterm2.com/documentation-escape-codes.html",
      "source_version": "iTerm2 docs, retrieved 2026-05-29",
      "note": "iTerm2 documents OSC 50 to set the session font (e.g. OSC 50 ; <font spec> ST), with its own spec syntax distinct from xterm's XLFD."
    }
  ],
  "see_also": [
    "terminal-osc/1337",
    "terminal-osc/4"
  ],
  "ext_type": "terminal-escape@1",
  "ext": {
    "csi_or_osc": "OSC",
    "command_number": 50,
    "frame": {
      "introducer_7bit": "\u001b]",
      "introducer_7bit_readable": "ESC ] (0x1B 0x5D)",
      "introducer_8bit": "",
      "introducer_8bit_readable": "0x9D (single-byte OSC, 8-bit C1)",
      "note": "OSC frame (ECMA-48). Command number 50 is a de-facto font-control number used by xterm and iTerm2 with differing spec syntax; no registry."
    },
    "terminator": "ST|BEL",
    "terminator_detail": {
      "canonical_ST_7bit": "\u001b\\",
      "canonical_ST_7bit_readable": "ESC \\ (0x1B 0x5C)",
      "canonical_ST_8bit": "œ",
      "canonical_ST_8bit_readable": "0x9C (single-byte ST, 8-bit C1)",
      "alt_BEL": "\u0007",
      "alt_BEL_readable": "BEL (0x07)",
      "note": "ECMA-48 mandates ST; xterm and most modern terminals also accept BEL. Emit ST, accept both."
    },
    "params": [
      {
        "id": "set",
        "anchor": "#set",
        "name": "Set font",
        "meaning": "OSC 50 ; spec ST sets the font. xterm: spec is an XLFD or '#N' to select a numbered font; iTerm2: its own font-spec syntax.",
        "required": true,
        "byte_sequence_ST": "\u001b]50;#3\u001b\\",
        "byte_sequence_ST_readable": "ESC ] 5 0 ; # 3 ESC \\   ==  \\x1b]50;#3\\x1b\\\\   (xterm: select font #3)",
        "byte_sequence_BEL": "\u001b]50;#3\u0007",
        "byte_sequence_BEL_readable": "ESC ] 5 0 ; # 3 BEL   ==  \\x1b]50;#3\\x07",
        "subparams": []
      },
      {
        "id": "query",
        "anchor": "#query",
        "name": "Query font (xterm)",
        "meaning": "OSC 50 ; ? ST asks xterm for the current font; it replies with the font name. (iTerm2 does not necessarily support the query.)",
        "required": false,
        "byte_sequence_ST": "\u001b]50;?\u001b\\",
        "byte_sequence_ST_readable": "ESC ] 5 0 ; ? ESC \\   ==  \\x1b]50;?\\x1b\\\\   (query current font)",
        "byte_sequence_BEL": "\u001b]50;?\u0007",
        "byte_sequence_BEL_readable": "ESC ] 5 0 ; ? BEL   ==  \\x1b]50;?\\x07",
        "subparams": []
      }
    ],
    "gotchas": [
      "The SPEC SYNTAX differs: xterm expects an XLFD or '#N' index; iTerm2 uses its own font-name form. The same OSC 50 is not portable between them.",
      "OSC 50 has also been used by some terminals (and DEC) for other purposes historically; treat support as terminal-specific and feature-detect.",
      "The query form is an xterm convention; do not rely on iTerm2 answering it.",
      "Changing the font may resize cells and reflow the screen; expect a resize event.",
      "Over tmux/ssh the sequence must be passed through to the outer terminal."
    ],
    "v1_smoke_test": {
      "asserts": "OSC 50 set (xterm '#N') and query forms render as byte-exact OSC strings; the xterm-vs-iTerm2 spec divergence is recorded.",
      "behavioral_conformance": "deferred to v2."
    }
  },
  "updated": "2026-05-29T00:00:00Z"
}