Comparison

SpeakCAD vs Shapr3D: CAD on a tablet with a pencil, or on a phone with a sentence

Shapr3D proved that serious CAD can live on a tablet. It is a direct-modelling tool with a professional geometry kernel, designed for an iPad and an Apple Pencil, and it is genuinely good. It is also a full CAD program to learn, it wants a stylus and a large screen, and its paid tiers are priced for professionals. SpeakCAD approaches mobile from the other side: no drawing at all, so a phone screen and a thumb are enough.
CriterionSpeakCADShapr3D
DevicesAny phone, tablet or computer with a browseriPad, Mac and Windows apps; iPad is the flagship
InputPlain-English chat, photos with a ruler, STL/3MF/.scad uploadsSketch and push-pull with Apple Pencil or mouse
Learning curveNone: describe, then say what to changeReal CAD: sketches, constraints, history-free direct modelling
InstallNone: runs in Safari or ChromeApp download; needs a capable iPad
PrecisionExact millimetres from your description; every dimension is a named parameterExact; professional Parasolid kernel
OutputSTL, 3MF, OpenSCAD sourceSTEP, STL, 3MF, OBJ, IGES and more (export limits on the free tier)
Organic shapesNo: functional parts onlyLimited: it is a solid modeller, not a sculptor
Best forFunctional 3D-printed parts in minutes, from wherever the part isDesigners who draw, need STEP, and work on an iPad
PriceFree to try; Maker $3.99/mo or Pro $7.99/moFree tier with limited designs and export quality; paid plans are yearly subscriptions priced for professionals (check their site)

Two answers to "CAD on a mobile device"

Shapr3D's answer is to make the tablet as good as a workstation: a fast kernel, a pencil for sketching, gestures for push-pull. It works because an iPad is large and precise enough to draw on. The cost is that it is still CAD: you learn sketching, dimensioning and Boolean operations, and you need the tablet and the pencil.

SpeakCAD's answer is to remove drawing. The part is described in a sentence with the numbers you measured; the AI writes a parametric program and the browser compiles it into a mesh. The interface that needs is a text box and a viewer, which fit on a phone. There is no pencil because there is no sketch.

Where Shapr3D wins

If you design by drawing, need STEP files for a machinist or an assembly, work on organic-ish surfaces with fillets you place by hand, or want a professional history-free modeller on an iPad, Shapr3D is the better tool and the free tier lets you find out. It also handles large assemblies in a way a text description never will.

Where SpeakCAD wins

If what you need is a bracket, a case, an organizer or a replacement part for a 3D printer, and you would rather not learn CAD or carry a tablet, describing the part takes three minutes on the phone in your pocket. Every dimension is a parameter you can change by chat afterwards, fits and printability rules are applied without being asked, and a fix after a test print re-downloads free. It also copies a part from two phone photos and a ruler, which no drawing tool does.

Using both

Shapr3D imports STL and OpenSCAD-derived meshes poorly, as any CAD does, but many makers use SpeakCAD for the ten-minute parts and Shapr3D for the one design a month that needs STEP or careful surfacing.

Your next print is one sentence away

Try it free: describe a part and watch it render, as many times as you like. Pick a plan when you want the file. Runs in your browser, nothing to install, no card, no CAD skills.