UXML Editor

Standalone visual editor for Unity UI Toolkit UXML and USS. The editor core is browser-first; Tauri 2 provides a thin Windows desktop host for native filesystem operations.

Editing is source-backed: every hierarchy, canvas, and inspector action is a patch against the original UXML/USS bytes, so comments, attribute order, and user formatting survive a round trip.

What works

• Projects — open a directory through the File System Access API in the browser or the native picker on desktop; enumerate, read, and save .uxml and .uss files with revision checks, external-change watching, and crash recovery.
• Canvas — Yoga-backed preview with selection, drag/resize manipulation, and static pseudo-state toggles.
• Hierarchy — reparent, reorder, insert, and delete elements from a palette of uxml-preview's renderers.
• Inspector — provenance-aware attribute and style authoring that shows which rule a computed value came from and writes to the matching source.
• Source — CodeMirror editing of the same documents, kept in sync with the visual views through one transaction/undo history.
• Diagnostics — parser and renderer warnings surfaced per document.

Not implemented

• Animation of any kind. USS transitions are parsed and preserved but never played; pseudo-state toggles are static.
• Unity 6.3 features. Rendering comes from the vendored uxml-preview 0.5.0 engine in vendor/uxml-preview, which is measured against Unity 6000.0.40f1 and has no filter, aspect-ratio, SVG, 9-slice, or text-outline support.
• Controls beyond VisualElement, Label, Button, Image, ScrollView, Toggle, TextField, IntegerField, FloatField, DropdownField, Slider, SliderInt, and Foldout. Unknown controls stay in the tree, render as fallback boxes, and raise a warning. Everything after ScrollView is built from Unity's documented element names and USS classes rather than from measurements, so captions, classes, and nesting are right but default sizes and spacing are not; each says so through a diagnostic.
• Atomic conditional replacement off Windows. The native replaceTextAtomically returns unsupported on other platforms; the browser host uses its own revision-checked write path.

Requirements

• Node.js >=24.15.0 <25, with npm
• Rust stable (desktop host)
• Windows: Visual Studio C++ build tools, the Windows SDK, and the WebView2 runtime
• Linux (host development only): libwebkit2gtk-4.1-dev, libgtk-3-dev, libsoup-3.0-dev, librsvg2-dev, libjavascriptcoregtk-4.1-dev, pkg-config

Commands

npm ci
npm run dev              # Vite dev server on :1420
npm run typecheck        # tsc --noEmit
npm test                 # Vitest unit and integration suites
npm run test:e2e         # Playwright, against the dev server
npm run test:rust        # cargo test for the desktop host
npm run check:licenses   # dependency license allowlist
npm run build            # typecheck + browser production build
npm run tauri:dev
npm run tauri:build      # Windows installer and portable artifacts
npm run smoke:packaged      # artifact + --version-file checks on the built exe
npm run smoke:packaged:app  # Windows: drives the packaged app over WebView2 CDP

CI runs the same commands on Linux and repeats the host tests plus a tauri build --no-bundle on Windows, which is the only platform that exercises the conditional-replacement implementation.

The packaged executable accepts --open <project-dir> (or a bare directory argument) to open a project on launch. smoke:packaged:app uses that flag plus UXML_EDITOR_CDP_PORT — an opt-in WebView2 remote-debugging port the app honors only when the variable is set — to drive a real open → save → edit → relaunch cycle against files on disk.

Architecture

src/core holds the host-agnostic editor: the source patch engine, document sessions, transactions, stable locators, UXML/USS commands, and the persistence/recovery layer. src/features holds the panels. src/app wires a host implementation (BrowserHost, MemoryHost, or the Tauri host in src-tauri) into the shell.

The preview engine is vendored source, not an npm dependency: vendor/uxml-preview holds uxml-preview 0.5.0 under Apache-2.0, with its upstream test suite, its license, and the import recorded in vendor/uxml-preview/PROVENANCE.md. It is vendored because Unity 6.3 parity, controls beyond its five renderers, and transition playback all need engine changes upstream has scoped out. npm test runs the upstream suite, so engine edits still have to satisfy the measurements they came from.

It is reachable from exactly one file, src/core/adapter/UxmlPreviewAdapter.ts; an import-boundary test enforces that, that the package is absent from dependencies, and that the app's TypeScript program stays free of Node typings.

Layering and the fidelity model are described in docs/architecture.md; what the preview can and cannot reproduce — including which controls are measured versus merely documented — is in docs/compatibility.md. Decisions are recorded in docs/adr.

License

Original code is licensed under Apache-2.0. See LICENSE and THIRD-PARTY-NOTICES.md.