Bun Runtime Pro

Bun Runtime Pro helps you build applications that lean on Bun's built-in runtime APIs instead of stitching together Node, npm, a bundler, and a test framework. It's for developers starting a new server, CLI, or library who want one toolchain — and for teams migrating an existing Node project onto Bun 1.x and replacing express, sqlite3, vitest, and pkg with native equivalents.

When to use it

• Spinning up an HTTP or WebSocket service and you want a zero-dependency server.
• Adding a local database without a native-module compile step (bun:sqlite ships in the runtime).
• Replacing Jest/Vitest with bun test and its Jest-compatible expect matchers.
• Shipping a CLI as a single self-contained executable via bun build --compile.
• Tightening dev loops with bun --hot instead of nodemon + ts-node.

What it does

It scaffolds and reviews code against the real Bun 1.x surface:

• HTTP / WebSocket: Bun.serve({ port, fetch, websocket }), returning standard Response objects, plus routes for path matching and server.upgrade(req) for WS.
• SQLite: import { Database } from "bun:sqlite", prepared statements via db.query(...).all()/.get()/.run(), and db.transaction().
• Testing: import { test, expect, describe, mock } from "bun:test", run with bun test --watch and --coverage.
• Packages & scripts: bun install (uses bun.lockb), bunx, and bun run.
• Bundling: Bun.build({ entrypoints, outdir, target }) and bun build --compile --target=bun-linux-x64.
• Env & files: automatic .env loading, Bun.file() / Bun.write().

Usage example

curl -fsSL --create-dirs -o ~/.claude/skills/bun-runtime-pro/SKILL.md https://claudeskil.com/skills/bun-runtime-pro/SKILL.md
bun init -y

// server.ts
import { Database } from "bun:sqlite";
const db = new Database("app.db");
db.run("CREATE TABLE IF NOT EXISTS hits (n INTEGER)");

Bun.serve({
  port: 3000,
  fetch(req) {
    db.run("INSERT INTO hits (n) VALUES (1)");
    const { c } = db.query("SELECT count(*) c FROM hits").get() as any;
    return new Response(`hits: ${c}`);
  },
});

bun --hot server.ts                 # hot reload
bun test --coverage                 # run tests
bun build server.ts --compile --outfile app   # single binary

Tips & gotchas

• bun --hot keeps state across reloads (the process isn't restarted); use bun --watch if you need a full restart.
• bun:sqlite is synchronous by design — no await on queries. Reuse prepared statements; don't rebuild db.query() in hot paths.
• --compile embeds the Bun runtime, so binaries are ~50MB+ and are platform-specific; cross-compile with --target.
• bun install reads bun.lockb (binary). Commit it, but expect package-lock.json to be ignored.

FAQ

Can I keep using npm packages? Yes. bun install resolves the npm registry; most CommonJS and ESM packages work unchanged.

Does it replace tsc? Bun executes .ts/.tsx directly (no emit), but it does not type-check — run tsc --noEmit in CI for that.

Node APIs? Most node: built-ins are polyfilled; check Bun's compatibility table for gaps before migrating.