Partmode

PartMode

Open-source, local-first parametric CAD for people and permissioned typed agents.

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PartMode is browser-based mechanical CAD built on OpenCascade WebAssembly, replicad, and three.js. It combines constrained sketches, editable feature history, exact B-rep evaluation, assemblies, drawings, and standard exchange formats in one application that runs without a desktop CAD installation.

It is built around a simple idea: human and agent changes should use the same canonical document model and exact kernel instead of parallel, opaque automation state. In a browser-approved session they can revise the same open project; the separate headless path uses its own account-owned document.

Local by default	Exact geometry	Shared model + kernel
Model anonymously in the browser. Optional hosted agent connectivity and headless document storage are separate, explicit choices.	OpenCascade evaluates solid B-rep geometry. The shaded three.js scene is a view of the result, not the source of truth.	People use the CAD interface. Agents use typed, permissioned operations against the same schema and kernel; browser-approved agents can edit the open project.

PartMode is free to use, inspect, modify, and self-host under the GNU AGPL v3 license.

See PartMode in 18 seconds

Open an editable template, make a human parameter edit, approve a typed agent change, rebuild the exact geometry, and export STEP.

The demo was captured locally from public source snapshot 8db0b804 using the production typed-agent protocol. The complete steps and evidence are in the capture notes.

What you can build

Area	Included capabilities
Parametric parts	Constrained sketches, dimensions and expressions, editable feature history, multiple solid bodies, direct edits, configurations, patterns, holes, threads, sheet-metal, and structural tools
Assemblies	Reusable part definitions, occurrences, mates, direct in-context component editing, exploded views, sections, dependency inspection, and assembly mass properties
Drawings	Exact OpenCascade hidden-line views; SVG and PDF sheets can carry document-owned dimensions, tolerances, notes, symbols, and tables, while DXF exports a restricted R12 orthographic or sketch geometry subset
Interchange	Editable PartMode project bundles, STEP import and export, plus STL, AMF, and 3MF mesh exports
Inspection	Measurements, geometry health, volume, surface area, material-driven mass properties, centers of mass, inertia tensors, and persistent topology evidence
Agent workflows	Hosted MCP tools for capabilities, inspection, queries, detached previews, revision-safe commits, browser artifacts, and opt-in server-headless STEP workflows

Templates are editable schema-5 starting projects, not decorative meshes. Exact capability coverage varies by template, and a failed rebuild is reported instead of being treated as valid geometry.

One document model, two authority paths