kSTEP

Type-safe Kotlin DSL for the STEP standard (ISO 10303).

Warning

kSTEP is in early, pre-release development (M2). The API is unstable and nothing is published to Maven Central or Homebrew yet; tagged releases (GitHub releases, see CHANGELOG) are pre-releases: v0.1.0 is source-only, from v0.1.1 on a JVM-only CLI zip without native bridges is attached. See Status for what actually works today.

Licensed under the Apache License, Version 2.0. See LICENSE.

Why kSTEP

LLMs are strong in popular, high-resource languages (Kotlin, Java, Python) but measurably weak at generating external, low-resource DSLs — and STEP’s native exchange format (Part 21, graphs of #123-style entity references) is a particularly hostile one to read or write directly.

kSTEP applies Typed Domain Grounding (TDG) — the pattern already validated by its sibling project, kUML: expose a domain as a type-safe, embedded Kotlin DSL with semantic validation and structured errors, so that both human developers and LLM agents can work in it reliably. The syntax stays Kotlin (high-resource); only the vocabulary is domain-specific, enforced by the type system. A strict type system, a compiler, and structured validation errors form a feedback loop the LLM can act on directly, without a separate benchmark or fine-tuning step. kSTEP compiles that DSL down to the neutral, standardized ISO 10303 exchange format.

Vision

kSTEP is not "just another CAD tool." The ambition is to cover the entire STEP standard (ISO 10303): CAD is the entry point, not the boundary. STEP also spans manufacturing (STEP-NC), electrical and electronics, kinematics, composites, FEM/simulation and plant/process data, each carved out as its own Application Protocol (AP242, AP238, AP210, AP209, and others). Those APs are the building blocks kSTEP intends to grow into.

It is the deliberate third way between classic, GUI-centric CAD suites and niche code-first CAD: code-first, AI-first and STEP-native instead of proprietary. It is the same thesis as its sibling project kUML in the UML/SysML space, applied to the engineering domain.

V1 deliberately starts narrow: a single Application Protocol (AP242), scoped down to product structure and metadata (see Roadmap and kSTEP-ADR-0001). Geometry was added afterwards as an optional layer.

Status

The current release is v0.2.0 (2026-10-22), a pre-release; the master branch carries further work listed under "Unreleased" in the CHANGELOG. What is in place:

• EXPRESS parser, semantic model and Kotlin code generation, with an AP242 V1 entity layer (kstep-core) and STEP Part 21 export/import.

• A Kotlin scripting host for *.kstep.kts files, the kstep command-line tool (export, import, render, asciidoc, mcp) and an MCP server.

• Optional geometry: an OpenCascade (OCCT) bridge, a PlaneGCS sketch solver and headless preview rendering. Both native bridges need system libraries and are not part of the release zip.

The wave-by-wave log is in Status; open points are in the Roadmap. Both say what is and is not verified.

Quickstart

Requires JDK 21. Build the command-line tool and export a product structure to a STEP Part 21 file (the native geometry bridges are optional and not needed for this):

./gradlew clean :kstep-cli:installDist

Save this script as bracket.kstep.kts:

val appCtx = applicationContext { application = "config control" }.getOrThrow()
val prodCtx = productContext {
    name = "engineering"; frameOfReference = appCtx; disciplineType = "mechanical"
}.getOrThrow()
val defCtx = productDefinitionContext {
    name = "engineering"; frameOfReference = appCtx; lifeCycleStage = "design"
}.getOrThrow()

val bracket = product("BRK-001") { name = "Bracket"; frameOfReference = setOf(prodCtx) }.getOrThrow()
val bracketFormation = productDefinitionFormation("BRK-001-F") { ofProduct = bracket }.getOrThrow()
val definition = productDefinition("BRK-001-D") {
    formation = bracketFormation
    frameOfReference = defCtx
}.getOrThrow()

stepFile(fileName = "bracket.step") {
    root(definition)
}

kstep-cli/build/install/kstep-cli/bin/kstep-cli export bracket.kstep.kts
# Exported 1 root(s) to bracket.step

The installed launcher is named kstep-cli; the documentation calls the command kstep. The same pipeline as a library, parsing an EXPRESS schema and generating Kotlin source:

import dev.kstep.express.codegen.ExpressKotlinCodeGenerator
import dev.kstep.express.semantic.ExpressSemanticModelBuilder

val schema = """
    SCHEMA example_schema;
      ENTITY product;
        id   : STRING;
        name : STRING;
      END_ENTITY;
    END_SCHEMA;
""".trimIndent()

val model = ExpressSemanticModelBuilder.build(schema)
println(
    ExpressKotlinCodeGenerator.generateFileSource(
        model.schemas.single(),
        "dev.kstep.generated.example",
    ),
)
// package dev.kstep.generated.example
//
// import kotlin.String
//
// public data class Product(
//   public val id: String,
//   public val name: String,
// )

More examples (validation, geometry, sketches, rendering, import) are in Usage.

Modules

Module	Purpose
kstep-core	Core DSL types, validation results and the generated AP242 V1 entity classes.
kstep-express	ANTLR4 EXPRESS parser, semantic model and Kotlin code generator.
kstep-step21	STEP Part 21 reader and writer for the AP242 entities.
kstep-script	Kotlin scripting host for *.kstep.kts scripts.
kstep-cli	Command-line entry point.
kstep-mcp	MCP server exposing the entity builders and Part 21 export as LLM tools.
kstep-geometry	Optional OpenCascade (OCCT) JNI bridge for B-Rep geometry.
kstep-constraints	Optional PlaneGCS bridge for 2D geometric constraints.
kstep-sketch	Constraint-sketch DSL.
kstep-shape	AP242 shape assignment: merges product structure with B-Rep solids.
kstep-render	Headless mesh projection and SVG/PNG/text/glTF rendering.
kstep-preview	Shared headless preview pipeline behind render and asciidoc.
kstep-docs:kstep-asciidoc	Asciidoctor pre-processing integration (kstep asciidoc).
kstep-viewer	Interactive OCCT shape viewer (Compose Desktop).
kstep-tests	Cross-module integration tests (Kotest).

Details per module: Modules.

Documentation

Document	Contents
Status	Wave-by-wave status log of what works and what is verified.
Modules	Per-module reference.
Building	Build, CI, and the optional OCCT, PlaneGCS, viewer and validator setups.
Releasing	How a release is cut.
Usage	Library and CLI usage, MCP server, scripts.
Usage: sketches	Sketches and edge selection.
Usage: naming	Persistent edge naming, undo/redo.
Usage: mirror, scale, shell	Mirror, scale, face and vertex selection, shell.
Usage: import	Reading a STEP file back.
Roadmap	V1 scope and open points.
CHANGELOG	Release history.
Architecture decisions	The ADRs.

Note	Source comments and error messages written before this split refer to the README sections "Building", "Status", "Usage" and "Roadmap". They now live in the files above, for example "README 'Building'" is docs/building.adoc.

License and attribution

kSTEP is licensed under the Apache License, Version 2.0 — see LICENSE.

The bundled EXPRESS grammar (kstep-express/src/main/antlr/dev/kstep/express/grammar/Express.g4) is vendored from lutaml/express-grammar and is BSD-2-Clause licensed (Ribose Inc.); see NOTICE for full attribution.

A small excerpt of the real AP242 EXPRESS schema (kstep-express/src/main/resources/dev/kstep/express/codegen/ap242-v1-entities.exp — nineteen declarations, mostly verbatim (two spots deliberately adapted), not the complete 2,122-entity schema) is copied from the official CAx-IF/MBx-IF-published ap242ed2_dis2_mim_lf_v1.101.exp (ISO TS 10303-442 AP242 EXPRESS MIM Long Form, v1.101, 2019); see NOTICE for full provenance, which parts are verbatim vs. adapted, and the precedent this rests on.

kstep-mcp depends on the official Model Context Protocol Kotlin SDK (io.modelcontextprotocol:kotlin-sdk-server, maintained by Anthropic in collaboration with JetBrains), which is MIT licensed — compatible with kSTEP’s Apache 2.0 license, not vendored or modified, pulled in as a normal Gradle dependency.

kstep-geometry’s native JNI shim (`kstep-geometry/src/main/cpp/kstep_occt_bridge.cpp) is compiled, at build time only, against a system-installed Open CASCADE Technology (OCCT) library (Ubuntu package libocct-*-7.9), licensed under LGPL-2.1-only with the Open CASCADE Exception 1.0 — see https://dev.opencascade.org/resources/licensing. No OCCT binary, header, or source is vendored in this repository, and this product does not currently bundle or redistribute any OCCT binary; see NOTICE and docs/adr/ADR-0005-occt-jni-bridge.adoc for the full license and provenance discussion.