svelte-check-rs

Sunset · September 5, 2026. This project is no longer maintained and the repository is archived. Use the official svelte-check for new and existing projects. The source, releases, and benchmarks remain available as a historical reference under the MIT license; no further fixes or releases are planned.

Why this project existed

I started svelte-check-rs in January 2026, before official svelte-check offered TSGO or incremental compilation. On my own workloads, early versions made checks more than ten times faster. That changed how often I could run them and how quickly I could get back to building. I shared the project hoping it would do the same for other Svelte developers.

Why sunset it now?

Official svelte-check now supports native TypeScript checking and incremental caching. Its implementation PR explicitly credits svelte-check-rs and svelte-fast-check as inspirations. Seeing those improvements reach the official tooling is a meaningful outcome for this project.

The September 2026 benchmarks still show a Rust performance advantage, but the practical gap has narrowed considerably. On a synthetic 500-component project, warm checks took 0.35 seconds upstream and 0.16 seconds in Rust. On Careswitch Web, the timings were 3.14 and 2.20 seconds, with materially different diagnostics that prevent an equivalent-checking speedup claim.

Maintaining a separate parser, transformer, source mappings, and integrations requires ongoing work to follow Svelte, SvelteKit, and TypeScript. That cost is no longer justified by the remaining speed advantage. The recommendation is now to use the official checker and focus compatibility and performance improvements there.

Moving to official svelte-check

Use svelte-check in sveltejs/language-tools and follow its current installation and CLI documentation.

• Replace the svelte-check-rs development dependency with svelte-check using your package manager.
• Replace svelte-check-rs in package scripts, CI jobs, and agent instructions with svelte-check. Keep any existing svelte-kit sync step.
• Review flags against upstream's documentation; Rust-specific options are not portable. Re-run checks and review diagnostics before relying on the migrated command.
• For native checking, follow upstream's TypeScript dependency instructions. --tsgo --incremental enables both native checking and caching, but has documented limitations, including Svelte files outside the tsconfig root. The newer --tsgo-experimental-api mode has different tradeoffs and is experimental. Choose the mode appropriate for your project rather than assuming diagnostic parity.

This sunset is not a claim that every project will produce identical diagnostics after switching. The benchmark notes record known differences from the real application we measured.

Thank you

A special thank you to Guillermo Rauch, who shared svelte-check-rs when it first launched. Having something I’d built reach him—and seeing him help introduce it to the wider community—was an honor. I’m grateful that he took the time to support it.

Small projects depend on people willing to give them a chance and spread the word. Guillermo’s support helped this one reach more people, and everyone who tried it, contributed, or shared what they learned helped it grow. Seeing the work eventually help inform improvements in Svelte’s official tooling makes this a particularly meaningful place to leave it.

Thank you also to the Svelte and language-tools maintainers, the TypeScript native compiler team, and the wider community whose work made this possible. Please bring future Svelte checking improvements and reproducible issues to the official project, following its contribution guidance.

— Mark Fayngersh (@pheuter)

Benchmarks

Median of 5 runs, measured 2026-09-05. svelte-check 4.7.6 vs svelte-check-rs 0.11.2.

Apple M4 Max · 48 GiB · macOS 27.0 · Node 24.20.0 · Bun 1.4.0.

All timed public-fixture runs reported 0 errors and 0 warnings.

Careswitch Web (private monorepo) has different diagnostic results: upstream TS7: 436 errors / 3 warnings; Rust: 2 errors / 551 warnings. These timings do not establish equivalent checking; no speedup claim is made for this workload.

The TS7 baseline is svelte-check --tsgo --incremental, with both tools using TypeScript 7.0.2. Cold runs clear checker caches; warm runs preserve them; repeated-edit runs change one typed TypeScript export's value after an untimed priming edit. These are separate CLI processes, not watch-mode updates. Results depend on the workload.

See methodology, reproduction commands, and raw samples for versions, diagnostic checks, and limitations.

Historical reference

The following documents the final release for existing users and anyone studying or forking the code. It is not a recommendation to install this unmaintained tool.

npm install -D svelte-check-rs

{
  "scripts": {
    "check": "svelte-check-rs"
  }
}

npx svelte-check-rs

curl --proto '=https' --tlsv1.2 -LsSf https://github.com/pheuter/svelte-check-rs/releases/latest/download/svelte-check-rs-installer.sh | sh

irm https://github.com/pheuter/svelte-check-rs/releases/latest/download/svelte-check-rs-installer.ps1 | iex

# Check current directory
svelte-check-rs

# Check specific directory
svelte-check-rs --workspace ./my-project

# Watch mode
svelte-check-rs --watch

# Different output formats
svelte-check-rs --output json
svelte-check-rs --output machine
svelte-check-rs --output human-verbose

npm install -D typescript@^6 @typescript/native@npm:typescript@^7.0.2

crates/
├── svelte-parser/        # Lexer + parser + AST types
├── source-map/           # Position tracking and mapping
├── svelte-transformer/   # Svelte → TypeScript transformation
├── svelte-diagnostics/   # A11y and component checks
├── tsgo-runner/          # tsgo process management
├── bun-runner/           # bun-managed Svelte compiler bridge
└── svelte-check-rs/      # CLI binary

# Build all crates
cargo build

# Run tests
cargo test

# Run clippy
cargo clippy --all-targets -- -D warnings

# Format code
cargo fmt

git clone https://github.com/sveltejs/svelte.git /tmp/svelte
SVELTE_REPO=/tmp/svelte cargo test -p svelte-parser test_upstream_svelte_parser_samples -- --ignored

License

MIT License - see LICENSE for details.