NeoSCAD and OpenSCAD: what's the same, and what NeoSCAD adds

NeoSCAD is a new implementation of OpenSCAD’s language, written in Rust. If you write .scad files today, the short version is: your models and libraries run as they are, and you get a set of tools around them that OpenSCAD doesn’t have. This post goes through both halves, and through the places where NeoSCAD still differs.

What stays the same #

• The language. NeoSCAD reads OpenSCAD’s language, and OpenSCAD’s own regression suite is its specification: 1,773 of its in-scope tests pass, and a change to NeoSCAD may not make a passing test fail.
• Your libraries. MCAD and OpenSCAD’s default Liberation fonts are built in. BOSL2 works from your library path as it does in OpenSCAD, and all 3,569 of BOSL2’s example and test files give the same echo output as the OpenSCAD nightly.
• The command line. neoscad model.scad -o model.stl works as you know it, with OpenSCAD’s export formats, -D variables, customizer parameter files (-p/-P) and camera options for PNG export.

// CSG.scad - Basic example of CSG usage

translate([-24,0,0]) {
    union() {
        cube(15, center=true);
        sphere(10);
    }
}

intersection() {
    cube(15, center=true);
    sphere(10);
}

translate([24,0,0]) {
    difference() {
        cube(15, center=true);
        sphere(10);
    }
}

What NeoSCAD adds #

Speed #

On the benchmark, 14 models rendered to STL on one Apple M4 Pro, NeoSCAD is about 3.8× faster than the OpenSCAD nightly with its Manifold backend once process startup is subtracted. The geometric mean with startup included is 4.9×. The page has the full table, the method and the caveats. You can also run the same benchmark on your own machine with neoscad bench, and submit the result to the community results.

A printability check #

neoscad check renders the model and reports what would go wrong on an FDM printer. Each finding says where it is and how to fix it:

• a solid that isn’t manifold, or breaks when written at STL’s 32-bit precision;
• pieces floating above the bed, and surfaces that would print fused;
• walls thinner than the nozzle or your minimum wall;
• overhangs steeper than your limit;
• parts that intersect, and a model that doesn’t fit your bed.

neoscad check part.scad --nozzle 0.4 --min-wall 1.2 --bed 256x256x256

Snapshots and measurements #

neoscad snapshot draws a model’s standard views as one dimensioned PNG sheet, and --issues paints the check’s findings onto it. neoscad measure reports volume, area, bounding box, centre of mass, distances between parts and cross-sections.

A warm render server #

neoscad serve keeps a model’s caches warm and re-renders only what an edit changed. On the gearbox model on the home page, an edit to one part re-renders in about 0.25 s. The macOS app is built on the same engine.

Tools for AI agents #

NeoSCAD is built to be driven by AI coding agents as well as people:

• An MCP server, neoscad mcp, which Claude Code, Cursor or any MCP client can use to evaluate, render, check, measure and snapshot a model.
• JSON output from every command (--format json).
• Resource limits, --limit time=… or memory=…, so a runaway model stops with an error instead of filling the machine. Like OpenSCAD, NeoSCAD sets no limits by default.

Editor support, formatting and tests #

• neoscad lsp is a language server: diagnostics and completion in any editor that speaks the Language Server Protocol.
• neoscad fmt formats .scad files, keeping comments, and checks on every file that the program is unchanged.
• neoscad test runs model tests: module test_*() in *_test.scad files, with // @expect lines.
• neoscad docs gives the reference for builtins, and for the modules and functions of a file.

Named parts #

With --enable part, part("name") { ... } names a piece of a model, so check and measure can report on it by name. It is a NeoSCAD extension, off by default, so files stay OpenSCAD-compatible unless you opt in.

In the browser #

NeoSCAD in your browser runs the same engine compiled to WebAssembly, on your machine, with nothing to install. It includes BOSL2 examples, and it can connect to your AI agent so the agent edits the model you have open while you watch.

Where NeoSCAD still differs #

We don’t know of a model where NeoSCAD is slower than the OpenSCAD nightly, but we have measured only so many. If you find one, or a model that gives a different result, please open an issue.

Try it #

NeoSCAD is open source under GPL-2.0-or-later, OpenSCAD’s licence, at github.com/neoscad/neoscad. It is an independent project, not affiliated with or endorsed by the OpenSCAD project, and it exists because of OpenSCAD’s language, examples and test suite.