What is the SBX file format?
.sbx files are internal support files generated by Adobe Illustrator when working with CJK (Chinese, Japanese, Korean) typography using the Tsume proportional spacing feature. Tsume is a Japanese typographic technique that tightens the whitespace around a full-width character, fitting it more naturally into mixed-width text.
When an .ai document uses Tsume settings, Illustrator automatically creates an .sbx sidecar file in the same folder. This file stores the computed kerning and spacing table data that Tsume requires. You do not open, edit, or move .sbx files manually - Illustrator manages them entirely on its own.
The format is a proprietary Adobe binary data file with no publicly documented structure or magic bytes, not intended for user interaction. If an .sbx file is deleted, Illustrator will typically regenerate it, though Tsume spacing may appear temporarily incorrect until it does so.
.sbx files appear only alongside documents that actively use CJK Tsume spacing. The extension is also shared by the ESRI ArcGIS shapefile spatial index, an unrelated sidecar file that accompanies .shp files in geographic information systems - context makes them easy to tell apart.
Security & safety
RISK: LOWAn SBX file is a small, passive data blob generated by Adobe Illustrator. It contains no executable code and cannot run on its own. Leaving it alongside an .ai file is safe; deleting it is also safe (Illustrator will regenerate or go without the Tsume data). Treat unknown .sbx files from untrusted sources with normal caution.
Format details
in a nutshell- ESRI Shapefile Spatial Index - ESRI ArcGIS generates a .sbx file alongside every .shp shapefile as a spatial index to speed up query and rendering - users do not open it directly.
- ScratchX Project File - ScratchX experimental extension platform uses .sbx for saved project workspaces.
Programs that open SBX files
Windows2 apps
Adobe Illustrator
Paid Do not open the .sbx directly - Illustrator reads it automatically when you open the accompanying .ai file that uses CJK Tsume text. 
Adobe Creative Cloud
Paid Same as Illustrator - Creative Cloud subscription provides access; the .sbx is managed automatically. 
macOS1 app
Adobe Illustrator
Paid Open the companion .ai file in Illustrator; the .sbx is read automatically for Tsume CJK spacing. Technical details
deep spec| File type | Proprietary Adobe binary sidecar data file |
| Developer | Adobe Systems Incorporated |
| Application | Adobe Illustrator (CJK Tsume typography feature) |
| Encoding | Binary |
| Container | Proprietary Adobe internal data blob |
| Compression | Unknown (not publicly documented) |
| Typical file size | 1 KB - 50 KB |
| Magic bytes | None documented; proprietary format with no public signature |
| Purpose | Stores Tsume proportional spacing (CJK kerning) tables for Japanese/Chinese/Korean type |
| File relationship | Sidecar file created automatically alongside .ai documents that use CJK Tsume settings |
| User interaction | None required; generated and managed automatically by Illustrator |
| Regeneration | Illustrator recreates the file if deleted; Tsume spacing may appear incorrect temporarily |
| Associated OS | Windows, macOS |
| Released | Late 1990s (Adobe Illustrator Japanese/CJK typographic features) |
| Latest version | Current with the installed Adobe Illustrator CC version |
SBX conversions
Community Q&A
asked by usersNo questions yet - be the first to ask about SBX files.
