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.agents/skills/bun-runtime/SKILL.md

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+---
+name: bun-runtime
+description: Bun as runtime, package manager, bundler, and test runner. When to choose Bun vs Node, migration notes, and Vercel support.
+origin: ECC
+---
+
+# Bun Runtime
+
+Bun is a fast all-in-one JavaScript runtime and toolkit: runtime, package manager, bundler, and test runner. Use this skill when working in or migrating to Bun.
+
+## Core Concepts
+
+- **Runtime**: Drop-in Node-compatible runtime (built on JavaScriptCore, implemented in Zig).
+- **Package manager**: `bun install` is significantly faster than npm/yarn; lockfile is `bun.lockb`.
+- **Bundler**: Built-in bundler and transpiler for apps and libraries.
+- **Test runner**: Built-in `bun test` with Jest-like API.
+
+## When to Use Bun vs Node
+
+- **Prefer Bun** for: new JS/TS projects, scripts where install/run speed matters, Vercel deployments with Bun runtime, and when you want a single toolchain (run + install + test + build).
+- **Prefer Node** for: maximum ecosystem compatibility, legacy tooling that assumes Node, or when a dependency has known Bun issues.
+
+## Quick Reference
+
+### Run and install
+
+```bash
+# Install dependencies (creates/updates bun.lockb)
+bun install
+
+# Run a script (package.json "scripts" or direct file)
+bun run dev
+bun run src/index.ts
+
+# Run a file directly
+bun src/index.ts
+```
+
+### Scripts and env
+
+```bash
+# Load .env and run
+bun run --env-file=.env dev
+
+# Inline env
+FOO=bar bun run script.ts
+```
+
+### Testing
+
+```bash
+# Run tests (Jest-like API)
+bun test
+
+# Watch mode
+bun test --watch
+```
+
+```typescript
+// test/example.test.ts
+import { expect, test } from "bun:test";
+
+test("add", () => {
+  expect(1 + 2).toBe(3);
+});
+```
+
+### API (runtime)
+
+```typescript
+// File I/O (Bun-native, fast)
+const file = Bun.file("package.json");
+const json = await file.json();
+
+// HTTP server
+Bun.serve({
+  port: 3000,
+  fetch(req) {
+    return new Response("Hello");
+  },
+});
+```
+
+## Migration from Node
+
+- Replace `node script.js` with `bun run script.js` or `bun script.js`.
+- Run `bun install` in place of `npm install`; most packages work. If something fails, try `bun install --backend=hardlink` or report upstream.
+- Use `bun run` for npm scripts; `bun x` for npx-style one-off runs (e.g. `bun x prisma generate`).
+- Node built-ins (`fs`, `path`, `http`, etc.) are supported; prefer Bun APIs where they exist for better performance.
+
+## Vercel and deployment
+
+- Vercel supports the Bun runtime. Set runtime to Bun in project settings or use the Bun build preset where available.
+- Build command: often `bun run build` or `bun build ./src/index.ts --outdir=dist`.
+- Install command: `bun install --frozen-lockfile` for reproducible deploys.
+
+## Best Practices
+
+- Use `bun.lockb` and commit it for reproducible installs.
+- Prefer `bun run` for scripts so env and lifecycle are consistent.
+- For TypeScript, Bun runs `.ts` natively; no separate `ts-node` needed.
+- Keep dependencies up to date; Bun and the ecosystem evolve quickly.
+
+## When to Use This Skill
+
+Use when: adopting Bun, migrating from Node, writing or debugging Bun scripts/tests, or configuring Bun on Vercel or other platforms.