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CLAUDE.md

Commands

Uses pnpm (install via corepack enable pnpm). Node >= 24 required.

  • pnpm dev — dev server on http://localhost:3000
  • pnpm build — production build (static site, output to docs/)
  • pnpm check — svelte-check type checking
  • pnpm lint / pnpm lint:fix — prettier + eslint
  • pnpm test:unit — vitest in watch mode; pnpm vitest run for a single pass
  • Single unit test: pnpm vitest run src/lib/util/serde.test.ts (or -t "test name")
  • pnpm test:e2e — Playwright tests in tests/; auto-starts the dev server on port 3000 (reuses one already running). pnpm test:e2e:ui / :debug for interactive runs
  • pnpm test — unit + e2e

Gotchas:

  • If .claude/worktrees/ contains repo copies, vitest picks up their test files too — scope with pnpm vitest run --dir src.
  • Local Playwright runs can be flaky under parallel workers; retry or use --workers=1 before assuming a real failure.
  • CI runs lint, check, unit tests, and Playwright (against a production build) on PRs to master.

Architecture

SvelteKit 2 + Svelte 5 (runes) SPA using @sveltejs/adapter-static. docs/ is build output (GitHub Pages convention) — never edit it. Routes: / (redirects), /edit (main editor), /view (read-only viewer).

State flow (the core of the app)

src/lib/util/state.svelte.ts is the single source of truth:

  • inputState — a $state rune holding State (code, mermaid config JSON, pan/zoom, etc.), initialized from localStorage key codeStore. All writes must go through the exported update functions (updateCode, updateCodeStore, updateConfig, replaceInputState, ...), which call persistAndProcess(): persist to localStorage → async re-validate via mermaid.parse → publish to validatedState. Reads inside update functions are wrapped in untrack so calling effects don't depend on the whole input state.
  • validatedState — read-only validated snapshot (adds error, errorMarkers, serialized, diagramType). Internal reads should use this, but it is never persisted or shared externally.
  • The serialized state is mirrored into the URL hash (debounced) — the URL is the sharing mechanism. src/lib/util/serde.ts encodes state as pako:<base64 deflate> (legacy plain-base64 supported). mermaid.ink PNG/SVG links, Kroki, and Mermaid Chart URLs are derived from it in urls.
  • App startup goes through initHandler() in src/lib/util/util.ts: migrations → load state from URL hash → optional gist/URL loading (fileLoaders/) → start URL-hash subscription → analytics.

Persistence

src/lib/util/persist.svelte.ts provides readJSON/writeJSON and a persisted() localStorage-backed rune, shared by state, migrations (migrations.svelte.ts), promos, and History. History (src/lib/components/History/historyState.svelte.ts) auto-saves a timeline of diagrams for the whole session (startAutoSave() in the edit page).

Rendering

src/lib/util/mermaid.ts wraps mermaid and registers the ELK and tidy-tree layout engines plus ZenUML at module load. View.svelte renders the diagram; panZoom.ts wraps svg-pan-zoom; "rough" hand-drawn mode uses svg2roughjs. Sample diagrams come from @mermaid-js/examples.

Editors

Two editor implementations behind Editor.svelte: Monaco for desktop (DesktopEditor.svelte; custom mermaid language, completions, and error markers in monacoExtra.ts) and CodeMirror for mobile (MobileEditor.svelte). Both edit either the diagram code or the mermaid config JSON depending on editorMode.

Security

States loaded from URLs pass through sanitizeConfig (state.svelte.ts), which detects unsafe mermaid config (XSS vectors, prototype pollution, secure keys) and asks the user before stripping it. Keep this in mind when touching anything that deserializes external state.

UI / styling

  • shadcn-svelte components live in src/lib/components/ui/ (bits-ui based, registry config in components.json) — treat as vendored; several lint rules are disabled there.
  • Tailwind CSS 4 (via @tailwindcss/vite).
  • Icons via unplugin-icons: import X from '~icons/material-symbols/...'; custom icons load from static/icons under ~icons/custom/*.
  • Path alias: $/* → src/lib/* (in addition to SvelteKit's $lib).

Environment / build quirks

  • Env vars use the MERMAID_ prefix (import.meta.env), read in src/lib/util/env.ts. Defaults in .env; copy to .env.local for local overrides. These control renderer URL (mermaid.ink), Kroki, analytics, and Mermaid Chart integration.
  • HMR is deliberately disabled — every change triggers a full page reload (see alwaysFullReload in vite.config.js) because HMR corrupts app state.
  • vite.config.js pins monaco/mermaid/codemirror into named vendor chunks for long-term caching — keep that intact when touching build config.

Conventions

  • ESLint enforces alphabetically sorted object keys in src/ for objects with 5+ keys (sort-keys/sort-keys-fix), plus typescript-eslint strict and unicorn rules.
  • Unit tests are colocated with source (*.test.ts in src/); vitest runs with jsdom and also supports in-source tests (import.meta.vitest). Playwright e2e specs live in tests/ and use data-testid constants from src/lib/constants.ts (TID).