What is the CWK file format?
.cwk is the native document format for ClarisWorks and its successor AppleWorks, Apple's all-in-one productivity suite for Macintosh and Windows. A single .cwk file can hold a word processor document, spreadsheet, database, presentation, vector drawing, or bitmap painting - the document type is encoded in the file header rather than indicated by the extension alone.
The format uses a proprietary binary structure with a fixed 4-byte signature (05 02 99 00) and big-endian byte ordering. On classic Mac OS, the HFS creator code BOBO in file metadata identifies the originating application. Windows versions of ClarisWorks (from 1993) produce files with the same binary signature.
ClarisWorks launched in 1991; Apple acquired Claris and rebranded the suite as AppleWorks 5 in 1999. The final release, AppleWorks 6.2.9, appeared in 2004. Apple stopped selling AppleWorks in 2007 and dropped support in macOS Lion (10.7, 2011). macOS Catalina (10.15, 2019) removed 32-bit application support, making AppleWorks entirely non-functional on modern systems.
Apple's Pages and Numbers apps can import .cwk word-processing and spreadsheet files, but database and drawing types have no modern importer. LibreOffice includes partial import support via a legacy filter. The extension .cws is sometimes used interchangeably for the same format.
Security & safety
RISK: LOWStatic proprietary document format from a discontinued app; no script execution capability. Main risk is data loss - format is increasingly unreadable without legacy software.
Format details
in a nutshellPrograms that open CWK files
Windows1 app
LibreOffice
Open-source File > Open - partial AppleWorks word processing import. No native Windows app fully opens .cwk. 
macOS3 apps
LibreOffice
Open-source File > Open - supports AppleWorks word processing .cwk files via built-in filter (partial); database/drawing types not supported. 
Apple Pages
Free File > Open, select .cwk. Works for word-processing mode only; other document types fail or import partially. 
Apple Numbers
Free File > Open, select a spreadsheet-type .cwk file. Only spreadsheet mode supported. 
Technical details
deep spec| Format type | Proprietary binary all-in-one document |
| Magic bytes | `05 02 99 00` at offset 0 |
| Byte order | Big-endian |
| Encoding | Binary |
| Document type encoding | Header byte: 1 = word processor, 2 = spreadsheet, 3 = database, 4 = graphics, 5 = presentation, 6 = painting |
| Mac creator code | `BOBO` (HFS/HFS+ metadata, classic Mac OS) |
| Typical file size | 11 KB - several MB (larger with embedded graphics) |
| Associated OS | macOS (classic through Mojave 10.14); Windows (discontinued) |
| Last functional macOS | Mojave (10.14) - Catalina (10.15) dropped 32-bit support, breaking AppleWorks |
| Import compatibility | Pages and Numbers import word-processor and spreadsheet types only; database and drawing types unsupported |
| Released | 1991 (ClarisWorks 1.0 for Macintosh) |
| Latest version | AppleWorks 6.2.9 (2004) - last version ever released; format frozen since then |
CWK conversions
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