`ts-r-check`

Type checker. Replaces tsc.

Alpha
On npm

ts-r-check type-checks a TypeScript project and prints diagnostics in tsc’s format, with tsc’s error codes. Like tsc, it writes JavaScript, source maps and declarations unless noEmit is set; --noEmit only checks. It is the least finished part of ts-r, and it follows one rule: no false positives first.

Check all five projects, total wall timeShorter is faster.

ts-r-check1,936 ms
tsc 7.0.23,044 ms

1.6× faster type checks

What switching looks like

ts-r-check reads the config you already have, so switching is a change to the command, not the project.

package.json

  "scripts": {
-   "typecheck": "tsc --noEmit -p tsconfig.json",
+   "typecheck": "ts-r-check --noEmit -p tsconfig.json",
  }

What works, and what doesn’t yet

Works today

Loading the project from tsconfig.json, including extends, with tsc’s config diagnostics
Module resolution that matches tsc’s on every resolution of the reference app
Assignability, calls and overloads, generics and inference, unions and narrowing
keyof, mapped, conditional and literal types; classes, declarations and unused-code checks
tsc’s output in both plain and pretty form, with tsc’s exit codes

Not yet

Octal escapes in strings (TS1487) only with --no-history; no “Did you mean” suggestions on regular expression errors (TS1369)
Some inference: contextual types through reverse mapped types
Some relation and narrowing results, mostly in TS2322, TS2339 and TS2345
420 of 12,750 of tsc’s conformance test variants still differ (3.3%)

Measured

Every run, on the same reference app as the home page, with the command and commit that recorded it.

ts-r-check against tsc 7.0.2

Type checking five public projects from the command line, cold (no saved history), against TypeScript 7.0.2's native tsc. Some of these repos do not type-check cleanly under TypeScript 7. ts-r-check reports exactly tsc's diagnostics on tRPC, date-fns and TypeORM; on Playwright it reports 2 extra, and on RxJS 6 extra and misses 5 of about 21,900 (2026-10-24, 087afc9). It also skips checks it does not implement yet, so these times will move as the checker grows.

Check all five projects, total wall timeShorter is faster, in ms

ts-r
Other tools

ts-r-check1,936 ms
tsc 7.0.23,044 ms

Cold check, wall timeShorter is faster, in ms

tRPC packages/server108 ms
date-fns pkgs/core226 ms
RxJS packages/rxjs462 ms
TypeORM packages/typeorm548 ms
Playwright592 ms

Cold check, peak memoryShorter is faster, in MB

tRPC packages/server117 MB
date-fns pkgs/core216 MB
RxJS packages/rxjs458 MB
TypeORM packages/typeorm377 MB
Playwright463 MB

Warm runs, and each repo's own TypeScript
Project	ts-r-check, saved history, nothing changed	The repo's own tsc
tRPC	23 ms	1,130 ms
date-fns	78 ms	324 ms
RxJS	57 ms	2,468 ms
TypeORM	126 ms	3,915 ms
Playwright	40 ms	4,754 ms

How we measured

Measured: Wall time with hyperfine (cargo xtask bench --repos), median of 5 runs; peak RSS of one extra run. Every tool checks the same wrapper tsconfig (noEmit, not incremental)
Machine: Apple M-series MacBook (macOS arm64, 16 cores, 48 GB), shared with other jobs while measuring; release build, 4 threads
Software: ts-r-check release build; TypeScript 7.0.2 (native tsc) pinned in bench/package.json; each repo's own TypeScript
Input: tRPC, date-fns, RxJS, TypeORM and Playwright at the commits pinned in bench/repos.toml
Command: cargo xtask bench --fetch-repos --repos trpc,date-fns,rxjs,typeorm,playwright && cargo xtask bench --repos trpc,date-fns,rxjs,typeorm,playwright --memory check-
Recorded in: commit 9c3a371

Correctness

Compared with the tool ts-r-check replaces, on its own tests and on real code.

tsconfig loading100%
49 of 49 configs match
tsc --showConfig on private-app. Commit 856e43d.
Module resolution100%
63,958 resolutions, 0 mismatches
tsc --traceResolution, 24 private-app configs. Recorded in crates/ts_r_resolver/AGENTS.md.
Binder diagnostics90.0%
418 of 464 tests exact; 1,720 of 1,839 diagnostics found
tsc 7.0.2 baselines for the binder's codes (12,783 variants). Commit 4224610.
Type checker96.7%
96.7% exact (all diagnostics and chains); 214 variants with a diagnostic tsc does not report, 22 of them in tests where tsc reports nothing
tsc 7.0.2 conformance baselines, 12,750 compared test variants. Commit 775ce97.

Command line

An excerpt of ts-r-check --help. You can also run it through the launcher as ts-r check.

Next to tsc

ts-r-check reads the same tsconfig.json and prints the same format, so editor problem matchers and CI annotations that parse tsc’s output work unchanged. An error from ts-r-check is very likely one tsc reports too, but a clean run doesn’t mean tsc is clean. Keep tsc in CI until ts-r-check covers the features your project uses.

ts-r-check --help

usage: ts-r-check [-p tsconfig.json] [options]