@rsvelte/svelte-check

@rsvelte/svelte-check

A Rust-powered drop-in replacement for svelte-check. Type-checks .svelte, .svelte.ts / .svelte.js, and the surrounding .ts / .js files in a Svelte project, and reports compiler warnings, A11y warnings, CSS warnings, and TypeScript diagnostics from a single CLI.

Early stage. Output and flags are stabilising. Not yet recommended for production CI gates without a fallback to the official svelte-check.

Install

npm install -D @rsvelte/svelte-check
# pnpm add -D @rsvelte/svelte-check
# yarn add -D @rsvelte/svelte-check

The package ships a small loader that resolves the right prebuilt native binary for your platform via optionalDependencies. Supported targets:

OS	Architecture
macOS	arm64, x64
Linux	x64 (glibc), arm64 (glibc)
Windows	x64 (MSVC)

If your platform isn't listed, please open an issue.

Usage

From your project root:

# Compiler + A11y + CSS diagnostics only (fast — no TypeScript)
npx rsvelte-check

# Plus TypeScript diagnostics via tsgo
npx rsvelte-check --tsgo

# Watch mode with incremental cache
npx rsvelte-check --tsgo --watch --incremental

Add it to your package.json:

{
  "scripts": {
    "check": "rsvelte-check --tsgo",
    "check:watch": "rsvelte-check --tsgo --watch --incremental"
  }
}

CLI flags

Flag	Description
--workspace <dir>	Project root to scan. Defaults to the current directory.
--output <format>	human, human-verbose (default), machine, machine-verbose, or github-actions.
--ignore <list>	Comma-separated path components to skip while walking the workspace.
--fail-on-warnings	Exit non-zero when any warning is reported (default: errors only).
--tsgo	Run tsgo (or tsc) against the generated overlay and surface TypeScript diagnostics. Implies --emit-overlay.
--tsconfig <path>	Base tsconfig.json for the overlay to extends.
--emit-overlay	Materialise .tsx shadow files + an overlay tsconfig under <workspace>/.svelte-check/ without running a type-checker. Useful for inspecting what gets handed to TS.
--compiler-warnings <list>	Per-code overrides, e.g. --compiler-warnings css-unused-selector:ignore,a11y-no-noninteractive-element-to-interactive-role:error.
--diagnostic-sources <list>	Restrict output to any subset of svelte, ts / js, css.
--incremental	Reuse <workspace>/.svelte-check/manifest.json between runs — unchanged files skip the overlay regeneration step.
--watch	Stay alive and re-check on file changes. Composes with --incremental.
--preserve-watch-output	In watch mode, don't clear the terminal between runs.

Run rsvelte-check --help for the authoritative list.

How it works

rsvelte-check walks your project, parses every .svelte file with the rsvelte compiler, and reports compiler / A11y / CSS warnings directly. For TypeScript diagnostics, it generates .tsx shadow files (via @rsvelte/svelte2tsx) plus an overlay tsconfig.json under .svelte-check/, then hands the overlay to tsgo (preferred) or tsc. Diagnostics are remapped back onto the original .svelte source via high-resolution source maps so error positions point at the line and column you actually wrote.

Highlights:

• SvelteKit-aware. Honours svelte.config.js's kit.files overrides; injects SvelteKit-generated kit-file augmentations for both .ts (real TS annotations) and .js (JSDoc) files.
• Incremental. A per-file overlay manifest and a per-file warning cache (<cacheDir>/warnings.json) make warm runs near-instant.
• Parallel compile. Files are compiled across rayon workers; the TS pass is the long pole.
• Watch mode. Composes with --incremental for an editor-like inner loop.

Compatibility status

• Compiler / A11y / CSS warnings — full coverage; matches the official svelte-check's set.
• TypeScript diagnostics via tsgo — covered for the standard project shapes (plain Svelte 5, SvelteKit). Edge cases around custom preprocessors are still being shaken out.
• LSP integration (editor hover / completion) — out of scope for this package. Wait on the upstream tsgo tsserver mode before assuming editor support.

If you hit a diagnostic the official svelte-check produces and this one doesn't (or vice-versa), please open an issue with a minimal repro.

Known limitations

• Same-name Foo.svelte.ts / Foo.svelte.js companion next to Foo.svelte (#800). When a module file shares a component's base name, import … from './Foo.svelte' resolves to the companion instead of the component, so the component's default export and <script module> named exports are reported missing (has no default export, Circular definition of import alias, declares 'X' locally, but it is not exported). This is standard TypeScript relative-module resolution — tsc and tsgo behave identically — and the official svelte-check only avoids it via a TypeScript language-server plugin (resolveModuleNameLiterals) that the native tsgo binary does not support. Workaround: don't put a same-name companion next to a component — give shared module-context code a distinct name (e.g. foo-helpers.ts), or import the component's <script module> exports directly from ./Foo.svelte. The rsvelte_lint linter ships an opt-in svelte/no-companion-module-shadow rule (off by default) that flags this pattern so you catch it before it surprises you.

Performance

rsvelte-check is part of the rsvelte project. The underlying compiler runs 2.1× faster single-threaded and 15.8× faster multi-threaded than the official JS compiler on a 3,654-file corpus. The TypeScript pass via tsgo dominates wall-clock time on most projects; the Svelte side rarely registers.

License

MIT