svelte-check-native

Blazing fast CLI type-checker for Svelte projects. Drop-in replacement for svelte-check — compatible flags, byte-identical output, same exit codes. Powered by Rust + tsgo. Made for:

• AI agents that need tight feedback loops
• Fast CI/CD pipelines
• Git pre-commit hooks that actually stay enabled

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 'js,svelte'

  tool                  cold     warm     dirty   speedup   errors/warnings/problems
──────────────────────────────────────────────────────────────────────────────────────
svelte-check-native      2.5s     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:

Flags

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

New Flags

--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 — not supported.

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)

Monorepos

Pointed at a pnpm/npm/yarn workspace root with no paths of its own ({ "extends": "tsconfig/base.json" } and a pnpm-workspace.yaml listing apps/* / packages/*), this binary auto-discovers each member's tsconfig.json and unions their compilerOptions.paths into the overlay. So import x from '$lib/foo' from apps/dashboard/src/... resolves to apps/dashboard/src/lib/foo, and the same alias from apps/api/src/... resolves to apps/api/src/lib/foo — without restructuring your tsconfig.

Tradeoff: when two members declare the SAME alias targeting DIFFERENT directories ($lib in apps/a vs apps/b), tsgo tries each in order. As long as module names don't collide across sub-apps the right one resolves; cross-app name collisions silently misresolve to the first-listed sub-app. Acceptable v0 — real monorepos rarely overlap module names across $lib trees.

This is an innovation beyond upstream svelte-check. Their --tsgo mode requires --tsconfig and refuses to auto-discover. For tighter parity (and predictable per-app diagnostics), invoke this binary per sub-app instead:

svelte-check-native --workspace apps/dashboard

Roadmap

• CSS support

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