Skip to content

FAQ

Short answers to the questions that come up first. Each one links to the page with the detail.

Is tsc-rs a drop-in replacement for tsc?#

No, not yet. Default JavaScript emit matches tsc on every test case that has a JavaScript oracle, but diagnostics, declaration emit and the command line surface are not at parity. The conformance report has the numbers and Limitations lists the differences you are most likely to meet.

What is it good for today?#

  • Transpiling. TypeScript and TSX to JavaScript, with output that matches tsc byte for byte on the default configuration. This path runs in production inside the bext engine.
  • Embedding. A transpile pipe, a type-check daemon, a WebAssembly build and Rust crates you can link.
  • Fast feedback. A first-pass type check and a language server that start quickly. Treat the result as advisory and keep tsc as the final word.
  • Tooling. Preserve modes that keep type syntax in the output, and import graph audits.

How is it different from SWC, oxc or esbuild?#

Those tools remove TypeScript types without checking them. They are transpilers, and very good ones. tsc-rs implements the rest of the compiler too: the binder, the type checker, declaration emit and a language server, and it measures all of it against tsc's own baselines.

If all you need is fast transpilation, those tools are mature choices. tsc-rs is for cases where you want the types understood, not only erased, in Rust.

What about Microsoft's native port of TypeScript?#

Microsoft is porting the TypeScript compiler to Go. It is the official implementation, and if your goal is simply a faster tsc, it is the one to follow.

tsc-rs is an independent implementation with a different focus: a Rust codebase that tools can link as a library, modes that tsc does not have (preserve modes, the JSON pipes), and a compiler small enough to ship as WebAssembly.

Which TypeScript version does it follow?#

The test oracle is the TypeScript repository's own baselines, vendored under tests/. The standard-library tests and recent diagnostic work are verified against TypeScript 6.0.3.

Does it write output when there are type errors?#

No. When the checker reports errors, tsc-rs 0.4.1 writes no output files, where tsc emits by default. Use --transpileOnly to emit without type checking.

tsc-rs reports an error that tsc does not. Is my code wrong?#

Probably not. The type checker is incomplete and has false positives: on the last full measurement its precision was 83.3% on the compiler suite and 86.3% on the conformance suite. If tsc accepts the code, trust tsc, and please open an issue with a small reproduction.

Are there prebuilt binaries?#

Not as GitHub releases yet. Today you build from source, or install the npm package, which ships a Linux x64 binary and follows its own release schedule.

Which platforms does it build on?#

Anywhere a stable Rust toolchain runs. The repository's release workflow builds for Linux x64 and arm64, macOS x64 and arm64, and Windows x64. On Linux x64 the workspace is configured to link with clang and lld.

How fast is it?#

On typescript.js, a 7.8 MB fixture, one same-session comparison measured tsc-rs parsing in 44.5 ms against 35.2 ms for oxc, and parsing plus semantic analysis in 96.0 ms against 97.9 ms. --fast-emit transpilation runs two to four times faster than the structured emit path. The benchmarks are in crates/tsc_rs_bench; see Testing and the harness to run them.

Can I try it without installing anything?#

Yes. The playground runs the compiler in your browser as WebAssembly.

Why is the repository called ts-rs when the tool is tsc-rs?#

The repository is benfavre/ts-rs. The binary, the crates (tsc_rs_*) and the npm package are all named tsc-rs.

What is the license?#

MIT. The repository also vendors the TypeScript test corpus and reproduces TypeScript's diagnostic messages; that material is Copyright Microsoft Corporation and licensed under Apache 2.0. See NOTICE in the repository.

How do I report a bug or a difference from tsc?#

Open an issue with the input, the tsc output and the tsc-rs output. A case that reduces to a few lines is the most useful kind. If you want to fix it yourself, start with Contributing.

Found a mistake on this page? Open an issue on GitHub.