Compatibility
tsz is close to tsc compatibility across diagnostics, emit, and editor behavior. The remaining work is concentrated in real-project compile readiness and the last release-gate gaps tracked below.
Currently tracking TypeScript 6.0.3.
Type Checking
The conformance suite compares tsz diagnostics with tsc on TypeScript's own compiler tests. This is the main signal for whether tsz agrees with tsc about types and errors.
12,583 of 12,585 compiler tests match tsc.
Emit
Emit compatibility means the generated output matches what TypeScript users expect from tsc. JavaScript emit and declaration emit are tracked separately because they fail for different reasons and matter to different users.
JavaScript emit is at 100.0% (1 skipped). Declaration emit is at 100.0% (11,862 skipped).
Language Service
The language-service suite checks editor-facing behavior: completions, hover, go-to-definition, diagnostics, and related workflows that developers feel in an IDE.
6,556 of 6,562 editor tests match the TypeScript suite.
Project compatibility
These rows track real project fixtures that tsc accepts. A green row means tsz completed the same project check; red or yellow rows identify the current compatibility blocker.
| utility-types | green | exit success | check | 5 files | 33 MiB peak |
| ts-essentials | green | exit success | check | 95 files | 32 MiB peak |
| RxJS | green | exit success | check | 240 files | 35 MiB peak |
| type-fest | green | exit success | check | 206 files | 34 MiB peak |
| ts-toolbelt | green | exit success | check | 242 files | 758 MiB peak |
| Zod | yellow | nonzero exit | check | 8 files | 288 MiB peak |
| Kysely | yellow | nonzero exit | check | 272 files | 971 MiB peak |
| type-challenges solutions | green | exit success | check | 78 files | 19 MiB peak |
| generated Vite app | green | exit success | check | 4 files | 36 MiB peak |
| generated Next app | green | exit success | check | 7 files | 36 MiB peak |
| large-ts-repo | red | timeout | timing | 6,061 files | — |
| Next.js full project | green | exit success | check | 1,396 files | 301 MiB peak |
| Valibot | red | timeout | check | 1,083 files | 2,132 MiB peak |
| MSW | yellow | nonzero exit | check | 156 files | 321 MiB peak |
| Comlink | yellow | nonzero exit | check | 3 files | 125 MiB peak |
| Effect | red | timeout | check | 363 files | 846 MiB peak |
| Drizzle ORM | red | timeout | check | 448 files | 716 MiB peak |
| ts-rest | yellow | nonzero exit | check | 30 files | 227 MiB peak |
| ofetch | yellow | nonzero exit | check | 7 files | 41 MiB peak |