svelte-check-native Svelte Themes

Svelte Check Native

Blazing fast svelte-check (<1.0s) built with Rust

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svelte-check-native

svelte-check-native

Blazing fast CLI type-checker for Svelte projects. Drop-in replacement for svelte-check — compatible flags, byte-identical diagnostics, same exit codes. Single Rust binary, powered by tsgo, incremental via tsbuildinfo. Built for AI agents, CI/CD, and pre-commit hooks that actually stay enabled.

Not an LSP, CSS linter, or formatter.

Speed

Measured on a SvelteKit + TypeScript monorepo with 1359 .svelte files (Svelte 5 runes), M1 Pro 8C, mean of 2 runs each:

svelte-check-native --tsconfig tsconfig.json --diagnostic-sources 'ts,svelte'

  tool                  cold     warm     dirty   speedup   errors/warnings/problems
──────────────────────────────────────────────────────────────────────────────────────
svelte-check-native      1.8s     1.0s     0.9s      41x           0/49/17
svelte-check            40.0s    41.0s    41.6s     1.0x           0/49/17
svelte-check --tsgo     18.3s    18.6s    17.9s     2.9x           1/49/18
svelte-check-rs         12.2s     5.5      4.4s     7.5x         732/44/261

Diagnostic counts match svelte-check with same flags.

Install

npm i -D svelte-check-native @typescript/native-preview

@typescript/native-preview is the tsgo binary — required at check time, never imported at runtime.

Use

npx svelte-check-native --workspace .

Or add it to package.json:

{
  "scripts": {
    "check": "svelte-check-native --workspace ."
  }
}

Same flags as svelte-check. See npx svelte-check-native --help.

How it works

Single Rust binary. Each .svelte file flows through a handful of crates in one process:

Crate What it does
parser Parses .svelte source into a Svelte-5 AST (script + template).
analyze Builds a SemanticModel — runes, prop shapes, bindings, scope — used by emit and lint.
emit Generates the .svelte.ts overlay tsgo will type-check. Imports rewritten so tsgo lands on it.
svn-lint Native Rust port of svelte/compiler's warning pass. Covers all known codes; no subprocess.
svelte-compiler Fallback bridge to the user's svelte/compiler over a persistent bun/node worker pool.
typecheck Owns the tsgo overlay tsconfig + the tsbuildinfo cache; invokes tsgo; maps diagnostics back.
core Shared types (spans, diagnostics, position maps) + the canonical TsConfig struct.
cli Entrypoint. Flag parsing, file discovery, output formatting, exit codes.

Flags

Every flag not listed below behaves the same as svelte-check.

New flags

--svelte-warnings <mode>      How to source Svelte compiler warnings:
                              native | bridge
                              native: rust port faster
                              bridge: js bridge same as svelte-check, slower by 1.5-2s
--timings                     Phase-by-phase wall-clock breakdown
--debug-paths                 Print resolved binaries, exit
--tsgo-version                Print tsgo version, exit
--tsgo-diagnostics            Print tsgo's perf/memory stats after the run
--emit-ts                     Print generated TypeScript per file, exit

Not supported

  • --watch / --preserveWatchOutput — use watchexec or your editor's file watcher externally.
  • --no-tsconfig — errors out. A tsconfig is required.
  • --incremental — always on. tsgo's tsbuildinfo handles it.
  • --tsgo — always on. Classic tsc is not wired up.
  • --diagnostic-sources css — accepted but no-op (a CSS language service isn't bundled). Roadmap below.

Run svelte-check-native --help for the full list.

Output defaults to machine when run from a coding-agent CLI: CLAUDECODE=1 (Claude Code), GEMINI_CLI=1 (Gemini CLI), or CODEX_CI=1 (OpenAI Codex CLI).

Environment variables

  • TSGO_BIN — override tsgo discovery; accepts an absolute path to a platform-native tsgo binary. Useful when @typescript/native-preview isn't in node_modules (e.g. a monorepo where tsgo lives elsewhere).
  • SVN_BRIDGE_WORKERS — number of svelte/compiler worker subprocesses. Default cores/2, capped at 8; tracks the perf-core count on Apple Silicon. Override if you hit IPC contention on very large core counts.
  • CLAUDECODE / GEMINI_CLI / CODEX_CI — any set forces machine output for agent-friendly parsing.

Exit codes

  • 0 — no errors (and no warnings if --fail-on-warnings)
  • 1 — errors detected (or warnings with --fail-on-warnings)
  • 2 — invocation error (bad flag, missing tsconfig, tsgo not found)

Roadmap

  • CSS lint diagnostics

Troubleshooting

Stale errors after editing tsconfig.json or path aliases — wipe the cache: rm -rf node_modules/.cache/svelte-check-native and re-run. The overlay config is regenerated from your live tsconfig on every run, but tsgo's tsbuildinfo can hold onto stale resolution state.

TS2321 "Excessive stack depth" on your own types — usually a UnionToRecord<T> that round-trips through UnionToTuple<T>[number]. Iterate T directly in the mapped-type key instead.

Prior art

  • svelte2tsx / svelte-check — transpiler + CLI whose output shape and flags we match. The .v5 fixture corpus from svelte2tsx is our parity gate.
  • tsgo — the Go-based TypeScript compiler that does the actual type-checking. Shipped as @typescript/native-preview.

License

MIT

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