What a JWW file actually is
Jw_cad has been in use since 1991 and its file format is the default currency of Japanese construction drawings.
What a JWW file actually is
Jw_cad is a free 2D CAD program written in Japan. It first shipped for MS-DOS in 1991 and has been developed ever since. It spread mainly because it was free: architecture practices, surveyors and subcontractors adopted it without paying licence fees, and .jww became the normal way drawings move around Japanese construction.
The format is Jw_cad's own on-disk layout, an MFC-serialised binary. Unlike DXF it was never meant as an interchange format. Inside are lines, arcs and ellipses, text with its font and rotation, filled polygons, points, and reusable blocks, all organised into Jw_cad's grid of 16 layer groups by 16 layers, each group carrying its own scale. Files from Ver 7 onward can also embed raster images.
The developer publishes a partial memo describing the layout, but it is explicitly incomplete and may change between versions. That gap is why most software outside the Jw_cad family reads .jww poorly or not at all.
When people reach for this
Nearly everyone arrives here for the same reason: someone sent them a .jww and nothing on the machine will open it.
A file landed in your inbox and nothing opens it
Jw_cad is Windows-only, and most people who get sent drawings never had a reason to install it. Drop the file on this page and it renders in the browser.
Sending it to someone who has never heard of JWW
Outside Japanese construction almost nobody has Jw_cad. A PDF or PNG saves everyone the explanation.
Putting the drawing in a document
PNG drops straight into a report or a slide deck. Reach for SVG instead if the page might be printed at A3 or the drawing scaled up.
The geometry has to move into other CAD software
DXF carries lines, arcs, layers and line types into AutoCAD and most other packages, and the geometry stays editable instead of arriving as an image. Blocks survive as real BLOCK and INSERT records rather than being exploded into loose lines, which matters if the drawing repeats a component a few hundred times. One caveat worth knowing: Jw_cad's own DXF import wants Shift-JIS text and only reads older DXF revisions reliably, so a file that round-trips fine through AutoCAD can still come back into Jw_cad with the text missing. Ver 10, released in 2025, finally added Unicode support.
Terms you will run into
- .jww
- What Jw_cad saves on Windows, and the only format this site reads.
- .jwc
- The DOS-era format. Its layout is different and documented, which is why other CAD packages often read .jwc but not .jww. Jw_cad itself still opens these, so you can re-save one as .jww.
- DXF
- Autodesk's exchange format — the thing nearly every other CAD program can open.
- Vector
- An arc is stored as a centre point, a radius and two angles, which are the values Jw_cad wrote. It prints exactly at any size. SVG, PDF and DXF all work this way.
- Raster
- PNG writes everything onto a fixed pixel grid. Blow it up past its rendered size and it goes blocky.
- Layer group
- Jw_cad stacks layers two levels deep — 16 groups of 16, so 256 in all — and each group carries its own scale.