Bun Review 2026: The All-in-One JavaScript Toolkit Tested

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Bun Review 2026: The All-in-One JavaScript Toolkit Tested

Bun showed up in 2022 as a demo that made people suspicious. A JavaScript runtime written in Zig, using JavaScriptCore instead of V8, claiming it could install packages faster than npm and run tests faster than Jest? Sure. Then 1.0 landed in September 2023, and the skepticism turned into actual adoption. Three years later, Bun is at the 1.3.x line, Windows support is native rather than a WSL workaround, and a real number of production apps are running on it.

So is it worth switching? I spent the last few weeks running Bun against Node 22 on the same machine, on the same projects, and I have opinions. This review covers what Bun actually does well, where it still trips, and who should bother.

What Bun Actually Is

The marketing line is "all-in-one JavaScript toolkit," which sounds like fluff until you look at what's in the binary. Bun is four tools bundled together:

• A runtime that executes JavaScript and TypeScript directly
• A package manager (bun install) that replaces npm, yarn, or pnpm
• A test runner (bun test) with a Jest-shaped API
• A bundler (bun build) with an esbuild-compatible interface

On top of that, it ships a pile of built-in APIs that would otherwise be separate dependencies: SQLite, Redis, S3, password hashing, a shell scripting layer, an HTTP server, and a WebSocket server. All of it is MIT licensed and free. There is no paid tier, no enterprise upsell, no seat-based pricing. Oven, the company behind it, makes money elsewhere.

That matters for the pricing question people keep asking. There isn't one. The cost of Bun is your time migrating, not your credit card.

The Runtime: Where the Speed Comes From

Bun's runtime is built on JavaScriptCore, the engine Apple uses in Safari. That's a deliberate choice. V8 is optimized for long-running server processes; JavaScriptCore has historically been tuned for fast startup and lower memory in short-lived contexts. Bun leans into that.

In practice, cold starts are the headline. A TypeScript script that takes Node + tsx roughly 180ms to boot runs in about 35ms under Bun. For CLI tools, serverless functions, and anything spun up per-request, that gap is the difference between "acceptable" and "noticeably snappy."

TypeScript and JSX run natively. No ts-node, no tsx, no build step, no --experimental-loader flags. You point Bun at a .ts file and it runs. That alone removes a layer of tooling from most projects.

The HTTP server

Bun.serve() is the piece most people benchmark first. It's a single function that gives you an HTTP server with routing, WebSocket upgrades, TLS, and HTTP/2 support. No Express, no Fastify, no http.createServer boilerplate.

In my tests on an M3 MacBook Pro, a hello-world Bun.serve() handled roughly 110,000 requests per second under wrk with four threads. The same handler in Node 22 topped out around 45,000. Synthetic, yes, and real applications with database calls close that gap considerably. But the ceiling is genuinely higher, and for I/O-bound API work you feel it.

Node compatibility

This is the part that decides whether Bun is usable for you. Bun implements the node: module namespace, so node:fs, node:path, node:crypto, node:stream, node:worker_threads, process, Buffer, and AsyncLocalStorage all work. In my experience, most npm packages run without modification