What slop-cad is

slop-cad is a parametric CAD tool for mechanical parts. You draw a flat sketch, state the relationships that must hold in it, and push the closed regions of that sketch into a solid. Change a number later and everything downstream is rebuilt to match.

It runs entirely inside a browser tab. There is no installer, no account, and no server holding your work.

The whole idea, in fourteen seconds: a rectangle and a circle, drawn roughly, closed into a profile, and pushed into a solid.

Why constraints

A dimension here is a rule the geometry has to obey. Say that two lines are parallel, that a hole is 12 mm across, that an edge is 40 mm long, and the solver moves the drawing until every one of those holds at once. It moves it again the moment you change one of them.

The effort of stating those rules comes first and the return on it comes later, which is why constraining a sketch can feel like busywork the first time. It pays off when the plate has to be 55 mm rather than 40. You retype the 40, the sketch re-solves, the solid is rebuilt from it, and the pocket you cut and the edges you rounded come along with it, without any of them needing your attention.

What a session looks like

1. Draw rough geometry. Precision at this stage is wasted effort.
2. Add constraints and dimensions until the sketch stops having any freedom left.
3. Extrude the closed profile into a solid.
4. Sketch on a face of that solid to add a boss or carve a pocket.
5. Round or chamfer the edges you want softened.
6. Export a mesh, or save the document to come back to.

Step 2 is the one that gets skipped, and it is the one that decides how the part behaves later. A sketch with freedom left in it moves in ways you did not ask for the first time you change something. The status foot counts that freedom, so you can see when there is none of it left.

Who it suits

It suits mechanical parts made of flat sketches pushed into solids: plates, brackets, housings, spacers, enclosures. Anything you would describe as "a profile, extruded, with some things added and some things cut away".

It does not suit surfacing, sheet metal unfolding, assemblies of multiple parts, simulation, or drafting. All of those are absent rather than half finished.

Where it stops

The page on what it will not do is the one to read before committing a project to this. The entries most likely to catch you out: assemblies go as far as holding one body against another, the exports are STL, OBJ and STEP, undo does not cover every kind of change, and saving is something you do rather than something that happens.

Where to go next

Open it	What you need, and what happens to your work
Build your first part	Fifteen minutes, ending in an exported solid
The interface, named	Every region of the screen and what it is called

Once you have the vocabulary, the tutorials build a fuller part step by step, the how-to guides answer single questions, and the reference lists everything exhaustively.