What is the 123DX file format?
A .123dx file is a 3D CAD model created with Autodesk 123D Design, a free consumer solid-modelling application offered by Autodesk from 2011 to early 2017. Despite its approachable interface, 123D Design supported genuine parametric solid modelling suitable for 3D printing, laser cutting, and hobbyist manufacturing.
Internally a .123dx file is a ZIP archive - renaming it to .zip and extracting it reveals XML metadata, binary geometry, textures, materials, and a full parametric edit history. The container uses standard DEFLATE compression with CRC-32 integrity checks per entry. File sizes typically range from 1 MB to 50 MB.
Autodesk discontinued the entire 123D product family between November 2016 and March 2017, directing users toward Tinkercad (browser-based, free) and Fusion 360 (professional). Autodesk Fusion 360 can import .123dx files through its Upload feature, converting them to Fusion 360 (.f3d) cloud format. The original installer for 123D Design 2.2.14 still circulates through archive sites for those needing direct access to legacy files.
For interoperability, 123D Design could export to STEP, STL, OBJ, and SAT, enabling geometry migration - without edit history - to other CAD packages.
Security & safety
RISK: LOWPassive ZIP-based CAD container; no executable content. Very low risk.
Format details
in a nutshellMAGIC BYTES · FILE SIGNATURE
OFFSET
00010203
HEX
504B0304
ASCII
PK··
Container is a ZIP archive; content XML/binary inside identifies it as 123D Design
Programs that open 123DX files
Windows2 apps
Autodesk Fusion 360
Freemium File → Upload (or Data Panel → Upload), select the .123dx file; Fusion converts it to a cloud-based design.
Autodesk 123D Design 2.2.14 (legacy offline installer)
Free Install last version (2.2.14); opens .123dx natively. No longer actively distributed by Autodesk. 
macOS1 app
Autodesk Fusion 360
Freemium Upload .123dx via File → Upload; converted to Fusion cloud format automatically.
Web1 app
Autodesk Fusion 360 (web app)
Freemium Upload .123dx via the Data Panel; Autodesk servers convert the file. Technical details
deep spec| File type | ZIP-based 3D parametric CAD model |
| Container | ZIP archive |
| Magic bytes | 50 4B 03 04 (ZIP local file header; first two bytes spell "PK") |
| Compression | DEFLATE per entry within the ZIP container |
| Integrity | CRC-32 per ZIP entry |
| ZIP contents | XML metadata, binary geometry data, textures, materials, full parametric edit history |
| Byte order | Little-endian (ZIP structure) |
| Typical size | 1 MB - 50 MB |
| Developer | Autodesk, Inc. |
| Final version | 123D Design 2.2.14 (last release before discontinuation) |
| Discontinuation | Entire Autodesk 123D product family discontinued November 2016 - March 2017 |
| Modern import path | Autodesk Fusion 360 Upload feature converts .123dx to F3D cloud format |
| Legacy export formats | STEP, STL, OBJ, SAT (geometry only, without parametric history) |
| Associated OS | Windows, macOS, iOS (123D Design app, all discontinued) |
| Released | 2011 (Autodesk 123D Design public beta) |
| Latest version | 2.2.14 (final release before discontinuation) |
123DX conversions
Community Q&A
asked by users
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Frequently asked questions
How do I open a .123dx file now that 123D Design is discontinued?
Upload it to Autodesk Fusion 360 (free tier available). Go to File → Upload, select the .123dx file; Fusion will convert it to a cloud design you can edit and export.
Can I convert .123dx to STL for 3D printing?
Yes - import into Fusion 360, then export as STL. If you still have 123D Design 2.2.14 installed, it can export STL directly.
Is 123D Design still available to download?
Autodesk officially discontinued it in 2017 and removed it from their site, but the final installer (version 2.2.14) still circulates on archive sites. Use with caution; no security updates.
What replaced Autodesk 123D Design?
Tinkercad (free, browser-based, simpler) for beginners, and Fusion 360 (freemium, full professional CAD) for more complex work. Both are from Autodesk.
Can I open .123dx on a Mac?
The legacy 123D Design app ran on macOS but is no longer supported. The recommended approach today is Fusion 360 on macOS, which accepts .123dx uploads.
References
1Autodesk 123D - Wikipediaen.wikipedia.org
2CAD Forum - 123D format overviewwww.cadforum.cz
