`OS/2` table

Stores OS/2 and Windows-specific metrics — weight class, width class, Unicode ranges, and embedding flags.

Scope

Format family: Shared SFNT
Table tag in JSON: OS/2

Specs

https://learn.microsoft.com/en-us/typography/opentype/spec/os2
OpenType table registry: https://learn.microsoft.com/en-us/typography/opentype/spec/otff#font-tables

JSON Skeleton

This skeleton reflects fields currently parsed/written by Font Flux JS for this table.

json

{
  "tables": {
    "OS/2": {
      "version": 0,
      "sTypoAscender": 0,
      "xAvgCharWidth": 0,
      "usWeightClass": 0,
      "usWidthClass": 0,
      "fsType": 0,
      "ySubscriptXSize": 0,
      "ySubscriptYSize": 0,
      "ySubscriptXOffset": 0,
      "ySubscriptYOffset": 0,
      "ySuperscriptXSize": 0,
      "ySuperscriptYSize": 0,
      "ySuperscriptXOffset": 0,
      "ySuperscriptYOffset": 0,
      "yStrikeoutSize": 0,
      "yStrikeoutPosition": 0,
      "sFamilyClass": 0,
      "panose": [],
      "ulUnicodeRange1": 0,
      "ulUnicodeRange2": 0,
      "ulUnicodeRange3": 0,
      "ulUnicodeRange4": 0,
      "achVendID": "ABCD",
      "fsSelection": 0,
      "usFirstCharIndex": 0,
      "usLastCharIndex": 0,
      "sTypoDescender": 0,
      "sTypoLineGap": 0,
      "usWinAscent": 0,
      "usWinDescent": 0,
      "ulCodePageRange1": 0,
      "ulCodePageRange2": 0,
      "sxHeight": 0,
      "sCapHeight": 0,
      "usDefaultChar": 0,
      "usBreakChar": 0,
      "usMaxContext": 0,
      "usLowerOpticalPointSize": 0,
      "usUpperOpticalPointSize": 0,
      "_checksum": 0
    }
  }
}

Top-level Fields

version - number (0..65535) [spec type: uint16]
sTypoAscender - number [spec type: FWORD]
xAvgCharWidth - number [spec type: FWORD]
usWeightClass - number (0..65535) [spec type: uint16]
usWidthClass - number (0..65535) [spec type: uint16]
fsType - number (0..65535) [spec type: uint16]
ySubscriptXSize - number [spec type: FWORD]
ySubscriptYSize - number [spec type: FWORD]
ySubscriptXOffset - number [spec type: FWORD]
ySubscriptYOffset - number [spec type: FWORD]
ySuperscriptXSize - number [spec type: FWORD]
ySuperscriptYSize - number [spec type: FWORD]
ySuperscriptXOffset - number [spec type: FWORD]
ySuperscriptYOffset - number [spec type: FWORD]
yStrikeoutSize - number [spec type: FWORD]
yStrikeoutPosition - number [spec type: FWORD]
sFamilyClass - number (-32768..32767) [spec type: int16]
panose - number[] [spec type: uint8]
ulUnicodeRange1 - number [spec type: uint32]
ulUnicodeRange2 - number [spec type: uint32]
ulUnicodeRange3 - number [spec type: uint32]
ulUnicodeRange4 - number [spec type: uint32]
achVendID - string (4-char tag) [spec type: Tag]
fsSelection - number (0..65535) [spec type: uint16]
usFirstCharIndex - number (0..65535) [spec type: uint16]
usLastCharIndex - number (0..65535) [spec type: uint16]
sTypoDescender - number [spec type: FWORD]
sTypoLineGap - number [spec type: FWORD]
usWinAscent - number [spec type: UFWORD]
usWinDescent - number [spec type: UFWORD]
ulCodePageRange1 - number [spec type: uint32]
ulCodePageRange2 - number [spec type: uint32]
sxHeight - number [spec type: FWORD]
sCapHeight - number [spec type: FWORD]
usDefaultChar - number (0..65535) [spec type: uint16]
usBreakChar - number (0..65535) [spec type: uint16]
usMaxContext - number (0..65535) [spec type: uint16]
usLowerOpticalPointSize - number (0..65535) [spec type: uint16]
usUpperOpticalPointSize - number (0..65535) [spec type: uint16]

Validation Constraints

version controls field presence and binary size (0 through 5 supported).
Legacy short v0 form (68-byte stop at usLastCharIndex) is supported when typo/win fields are omitted.
panose must be a 10-byte array.
For version >= 1, include code page range fields; for version >= 2, include x-height/cap-height/default/break/max-context fields; for version >= 5, include optical point size fields.

Authoring Example

json

{
	"tables": {
		"OS/2": {
			"version": 4,
			"xAvgCharWidth": 500,
			"usWeightClass": 400,
			"usWidthClass": 5,
			"fsType": 0,
			"panose": [2, 11, 6, 4, 2, 2, 2, 2, 2, 4],
			"achVendID": "NONE",
			"usFirstCharIndex": 32,
			"usLastCharIndex": 65535,
			"sTypoAscender": 800,
			"sTypoDescender": -200,
			"sTypoLineGap": 0,
			"usWinAscent": 1000,
			"usWinDescent": 250,
			"ulCodePageRange1": 1,
			"ulCodePageRange2": 0,
			"sxHeight": 500,
			"sCapHeight": 700,
			"usDefaultChar": 0,
			"usBreakChar": 32,
			"usMaxContext": 2,
			"_checksum": 0
		}
	}
}

Additional Nested Keys Seen In Implementation

version
xAvgCharWidth
usWeightClass
usWidthClass
fsType
ySubscriptXSize
ySubscriptYSize
ySubscriptXOffset
ySubscriptYOffset
ySuperscriptXSize
ySuperscriptYSize
ySuperscriptXOffset
ySuperscriptYOffset
yStrikeoutSize
yStrikeoutPosition
sFamilyClass
panose
ulUnicodeRange1
ulUnicodeRange2
ulUnicodeRange3
ulUnicodeRange4
achVendID
fsSelection
usFirstCharIndex
usLastCharIndex
sTypoAscender
sTypoDescender
sTypoLineGap
usWinAscent
usWinDescent
ulCodePageRange1
ulCodePageRange2
sxHeight
sCapHeight
usDefaultChar
usBreakChar
usMaxContext
usLowerOpticalPointSize
usUpperOpticalPointSize

Notes

Preserve _checksum for stable round-tripping.
If a table is only partially understood, prefer keeping unknown bytes in _raw instead of dropping data.
Validate with .validate() after edits.

OS/2 table ​

Scope ​

Specs ​

JSON Skeleton ​

Top-level Fields ​

Validation Constraints ​

Authoring Example ​

Additional Nested Keys Seen In Implementation ​

Notes ​