--- title: Bun v1.4.3 adds bun check, a built-in TypeScript type... description: Bun v1.4.3 introduces bun check, a native Rust-based TypeScript type checker built into the runtime that passes 100% of TypeScript 7.0.2's conformance suite... canonical: https://daily.dev/posts/bun-v1-4-3-adds-bun-check-a-built-in-typescript-type-checker-yjjoukrmc twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Bun v1.4.3 adds bun check, a built-in TypeScript type checker | daily.dev og:description: Bun v1.4.3 introduces bun check, a native Rust-based TypeScript type checker built into the runtime that passes 100% of TypeScript 7.0.2's conformance suite... og:url: https://daily.dev/posts/bun-v1-4-3-adds-bun-check-a-built-in-typescript-type-checker-yjjoukrmc og:image: https://api.daily.dev/og/posts/yJjoukrmC.png og:image:alt: Bun v1.4.3 adds bun check, a built-in TypeScript type checker og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Bun v1.4.3 adds bun check, a built-in TypeScript type checker **[Collections](https://daily.dev/sources/collections)** · 2 min read · 17 upvotes · 4 comments ## Summary Bun v1.4.3 introduces bun check, a native Rust-based TypeScript type checker built into the runtime that passes 100% of TypeScript 7.0.2's conformance suite while being 3x to 6.4x faster than tsc and using 2.2x to 4.9x less memory. It integrates with bun run, bun build, and bun test via --check flags, and also supports runtime type checks unlike traditional TypeScript tooling. The release also cuts idle CPU use by 67-89%, adds new APIs like Bun.FetchSession and experimental Bun.ModuleGraph, speeds up node:http responses up to 2.7x, and patches security issues including CVE-2026-48618 and HTTP/2 rapid reset vulnerabilities alongside numerous Node.js compatibility fixes. ## Content Bun v1.4.3 fixes 166 issues, and its headline feature is `bun check`, a TypeScript type checker built into the runtime and written in Rust. ## bun check Bun's pitch is that types are the first step toward ahead-of-time compiled TypeScript that can compete with languages like Go on memory and speed. `bun check` is that first step. It passes 100% of TypeScript 7.0.2's conformance suite. Compared with `tsc`, it runs 3x to 6.4x faster and uses 2.2x to 4.9x less memory. You can also run it as part of other commands with `--check` flags on `bun run`, `bun build`, and `bun test`. The developer @housecor called built-in type checks another compelling reason to consider Bun, and pointed to runtime checks as something traditional TypeScript doesn't offer. ## Runtime changes - Idle CPU use drops by 67-89%. - `Bun.FetchSession` is a new API for isolated connection pools. - `Bun.ModuleGraph` is experimental and aimed at multi-tenant apps. - `--disallow-code-generation-from-strings` is now supported. - Large `node:http` responses are up to 2.7x faster. - The JavaScriptCore upgrade brings faster `JSON.parse` and array operations. - Rejected promises are handled in linear time. - `CompressionStream` levels are configurable. - `Bun.serve` supports `If-Range`. ## Install and build `bun install` now skips tarball downloads it doesn't need. `bun build` uses less memory when there are many entry points and supports wider `[hashN]` output names. Executables built with `--compile --bytecode` get profile-guided layout and start faster. ## Security and compatibility The release hardens several TLS and certificate verification paths, including a fix for CVE-2026-48618, and patches the HTTP/2 rapid reset CVEs. It also includes dozens of compatibility fixes across `node:http`, `node:http2`, `node:tls`, and `node:net`. ## Questions this post answers ### What does the bun check command do in Bun 1.4.3? It is a built-in TypeScript type checker written in Rust, shipped in Bun 1.4.3, that passes 100% of TypeScript 7.0.2's conformance suite. It runs 3x to 6.4x faster than tsc while using 2.2x to 4.9x less memory, and it plugs into bun run, bun build, and bun test via --check flags. It also supports runtime type checks, which traditional TypeScript tooling does not. _Developers tracking faster alternatives to tsc can follow Bun's type-checking changes on daily.dev._ ### Which CVEs does Bun 1.4.3 patch? Bun 1.4.3 fixes CVE-2026-48618, a TLS and certificate verification issue, and patches the HTTP/2 rapid reset vulnerabilities. The release also hardens several other TLS and certificate verification paths and includes dozens of compatibility fixes across node:http, node:http2, node:tls, and node:net. _Teams patching Bun deployments against known CVEs can keep tabs on these fixes via daily.dev._ ### How much does idle CPU usage drop in Bun 1.4.3? Idle CPU usage drops by 67-89% in Bun 1.4.3, alongside a JavaScriptCore upgrade that speeds up JSON.parse and array operations, up to 2.7x faster large node:http responses, and linear-time rejected-promise handling. _Anyone benchmarking runtime efficiency before an upgrade can follow Bun's performance changes on daily.dev._ ## Community discussion Top comments from developers on daily.dev. **@sayidinaahmadalqososyi** · 0 upvotes > That’s interesting. i’ve been having issues with the project I’m currently working on, it keeps running into OOM errors. **@andrei0x309** · 0 upvotes > Great is speedy but it's not a replacement for tsc, would be nice if bundlers like vite could use it then it could actually improve the bundler speed. **@harshitmanepally** · 0 upvotes > Can't you explain what bun is before going into version updates and fixes. **@diyweb** · 0 upvotes > Speed matters most in the edit loop, where waiting on type checks hurts the most, so a 3x to 6.4x gain is worth noticing. I would still keep tsc in CI as the reference until bun check has been tested on larger monorepos with the full range of tsconfig options. ## Similar posts on daily.dev - [Bun v1.3.12](https://daily.dev/posts/bun-v1-3-12-f5ph0rgqu) · Bun · 140 upvotes · 2 comments - [Bun: a faster JavaScript runtime](https://daily.dev/posts/bun-a-faster-javascript-runtime-hnnh26fm5) · Flavio Copes · 0 upvotes · 0 comments - [Bun: A fast JS runtime Node.js replacement with built‑in tools](https://daily.dev/posts/bun-a-fast-js-runtime-node-js-replacement-with-built-in-tools-mufqlbhlc) · Product Hunt · 0 upvotes · 0 comments --- Tags: [#javascript](https://daily.dev/tags/javascript), [#typescript](https://daily.dev/tags/typescript), [#bun](https://daily.dev/tags/bun) [View this post on daily.dev](https://daily.dev/posts/bun-v1-4-3-adds-bun-check-a-built-in-typescript-type-checker-yjjoukrmc) ```json 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I would still keep tsc in CI as the reference until bun check has been tested on larger monorepos with the full range of tsconfig options.","datePublished":"2026-10-12T12:30:00.724Z","url":"https://daily.dev/posts/yJjoukrmC#c-XdngwXbRK","author":{"@type":"Person","name":"DiyWeb","url":"https://daily.dev/diyweb","image":"https://media.daily.dev/image/upload/s--dgS6jDeN--/f_auto/v1790879420/avatars/avatar_774zDwMaRTNS1fv5OKStX?_a=BAMAMicg0"}}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/bun-v1-4-3-adds-bun-check-a-built-in-typescript-type-checker-yjjoukrmc#faq","mainEntity":[{"@type":"Question","name":"What does the bun check command do in Bun 1.4.3?","acceptedAnswer":{"@type":"Answer","text":"It is a built-in TypeScript type checker written in Rust, shipped in Bun 1.4.3, that passes 100% of TypeScript 7.0.2's conformance suite. 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