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 TypeScript 7's native tsc. 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      2.5s     0.2s     0.9s      40x           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@^7.0.0

TypeScript 7 provides the native tsc binary required at check time; it is never imported at runtime. @typescript/native-preview (tsgo, the nightly channel) works too, as the fallback when typescript 7+ isn't installed — so you can keep typescript@6 for your own toolchain and check with tsgo. TypeScript 6 and below is never used as the check engine.

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 | Semantic passes — runes, prop shapes, events, bindings, scope — feeding emit and lint. | | emit | Generates the .svelte.ts overlay TypeScript will type-check. Imports rewritten so tsc 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 TypeScript overlay tsconfig + the tsbuildinfo cache; invokes tsc; 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.
• --tsgo — always on. TypeScript 7's native tsc is used.
• --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 Claude Code (CLAUDECODE=1), as upstream's does.

Environment variables

• TSGO_BIN — override discovery; accepts an absolute path to a platform-native tsgo/tsc binary or JS wrapper. Useful when neither engine package is in node_modules (e.g. a monorepo where TypeScript 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=1 — makes machine the default output format.
• NO_COLOR / FORCE_COLOR — turn colour off / on, as for upstream.

Android (Termux)

svelte-check-native's linux-arm64 binary is static, so it installs and runs on Android too. TypeScript 7 doesn't publish an Android build, so npm skips its native compiler there. Its linux-arm64 build runs fine on Android; install it explicitly:

npm i -D --force @typescript/typescript-linux-arm64@<your typescript version>

Or point TSGO_BIN at any Linux arm64 tsc/tsgo binary.

Exit codes

• 0 — no errors (and no warnings if --fail-on-warnings)
• 1 — errors detected (or warnings with --fail-on-warnings), or the TypeScript compiler did not complete (killed, or exited without a diagnostic), as svelte-check reports it
• 2 — invocation error (bad flag, missing tsconfig, TypeScript not found)

Roadmap

• [ ] CSS lint diagnostics

Troubleshooting

Stale errors with --incremental — wipe the cache: rm -rf node_modules/.cache/svelte-check-native and re-run. tsgo's tsbuildinfo can hold onto stale results; runs without --incremental (the default, as upstream) never read it.

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.
• TypeScript 7 — the native compiler that does the actual type-checking.

License

MIT