What it does:
- Parses Svelte files with a custom Rust parser - Transforms them to TSX in parallel using Rayon - Runs type-checking via Microsoft's tsgo (the native Go port of TypeScript) - Maps errors back to original .svelte locations via source maps
Why it's fast:
The official svelte-check uses TypeScript's Language Service API optimized for IDEs with persistent connections. Great for autocomplete but slow for batch CLI checks.
svelte-check-rs writes real TSX files to disk and runs tsgo as a standalone compiler. This enables incremental builds with persistent .tsbuildinfo, so subsequent runs only re-check changed files.
Benchmarks on a 650-file SvelteKit monorepo (M4 Max):
Cold: 17.5s vs 39.6s (2.3x faster)
Warm: 1.3s vs 39.4s (30x faster)
Iterative: 2.5s vs 39.8s (16x faster)
I built this in ~2 days using Claude Code (Opus 4.5) and Codex CLI (GPT-5.2 xhigh). The entire Svelte parser, TSX transformer, diagnostics engine, and CLI were written entirely by AI. I focused on architecture decisions and testing against real codebases while the models handled the implementation.
My motivation was actually to make AI coding agents more effective. When agents write code, they need to verify it works, and waiting 40 seconds for type-checking kills the feedback loop. With 1-2 second checks, agents can iterate much faster and catch their own mistakes immediately on our large and growing production SvelteKit codebase.
Website: https://svelte-check-rs.vercel.app/
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