Bun Runtime and Toolkit
mweinbach/agent-coworker
Quick reference for using Bun to run TypeScript and JavaScript, install packages, bundle code, run tests and serve HTTP, with the key files and commands.
A skill your agent uses for Bun runtime, bunfig.toml, watch/hot modes, env vars, CLI flags, and module resolution.
Install Bun Runtime
$ npx skills add secondsky/claude-skills --skill bun-runtime -a claude-codeProject install by default; add -g for ~/.claude/skills/.
$ gh skill install secondsky/claude-skills bun-runtime --agent claude-codeProject scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).
$ git clone --depth 1 https://github.com/secondsky/claude-skills.git skills-src && mkdir -p .claude/skills && cp -r skills-src/plugins/bun/skills/bun-runtime .claude/skills/bun-runtime && rm -rf skills-srcUse ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.
Claude Code skills documentation · loads skills from .claude/skills/
Install the "bun-runtime" agent skill from https://github.com/secondsky/claude-skills/tree/main/plugins/bun/skills/bun-runtime into .claude/skills/bun-runtime/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "bun-runtime", then confirm the skill loads.Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$skill-installer install https://github.com/secondsky/claude-skills/tree/main/plugins/bun/skills/bun-runtimeType this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.
$ npx skills add secondsky/claude-skills --skill bun-runtime -a codexProject install goes to .agents/skills/; add -g for ~/.codex/skills/.
$ gh skill install secondsky/claude-skills bun-runtime --agent codexProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/secondsky/claude-skills.git skills-src && mkdir -p .agents/skills && cp -r skills-src/plugins/bun/skills/bun-runtime .agents/skills/bun-runtime && rm -rf skills-srcUse ~/.agents/skills/ instead of .agents/skills for a personal install.
Codex skills documentation · loads skills from .agents/skills/
Install the "bun-runtime" agent skill from https://github.com/secondsky/claude-skills/tree/main/plugins/bun/skills/bun-runtime into .agents/skills/bun-runtime/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "bun-runtime", then confirm the skill loads.Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add secondsky/claude-skills --skill bun-runtime -a cursorProject install goes to .agents/skills/; add -g for ~/.cursor/skills/.
$ gh skill install secondsky/claude-skills bun-runtime --agent cursorProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/secondsky/claude-skills.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/plugins/bun/skills/bun-runtime .cursor/skills/bun-runtime && rm -rf skills-srcUse ~/.cursor/skills/ instead of .cursor/skills for a personal install.
Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/
Install the "bun-runtime" agent skill from https://github.com/secondsky/claude-skills/tree/main/plugins/bun/skills/bun-runtime into .cursor/skills/bun-runtime/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "bun-runtime", then confirm the skill loads.Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gemini skills install https://github.com/secondsky/claude-skills.git --path plugins/bun/skills/bun-runtime--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.
$ npx skills add secondsky/claude-skills --skill bun-runtime -a gemini-cliProject install goes to .agents/skills/; add -g for ~/.gemini/skills/.
$ gh skill install secondsky/claude-skills bun-runtime --agent gemini-cliProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/secondsky/claude-skills.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/plugins/bun/skills/bun-runtime .gemini/skills/bun-runtime && rm -rf skills-srcUse ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.
Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/
Install the "bun-runtime" agent skill from https://github.com/secondsky/claude-skills/tree/main/plugins/bun/skills/bun-runtime into .gemini/skills/bun-runtime/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "bun-runtime", then confirm the skill loads.Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gh skill install secondsky/claude-skills bun-runtimeInstalls for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).
$ npx skills add secondsky/claude-skills --skill bun-runtime -a github-copilotProject install goes to .agents/skills/; add -g for ~/.copilot/skills/.
$ git clone --depth 1 https://github.com/secondsky/claude-skills.git skills-src && mkdir -p .github/skills && cp -r skills-src/plugins/bun/skills/bun-runtime .github/skills/bun-runtime && rm -rf skills-srcUse ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.
GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/
Install the "bun-runtime" agent skill from https://github.com/secondsky/claude-skills/tree/main/plugins/bun/skills/bun-runtime into .github/skills/bun-runtime/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "bun-runtime", then confirm the skill loads.GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add secondsky/claude-skills --skill bun-runtime -a opencodeOpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.
$ gh skill install secondsky/claude-skills bun-runtime --agent opencodeProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/secondsky/claude-skills.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/plugins/bun/skills/bun-runtime .opencode/skills/bun-runtime && rm -rf skills-srcUse ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.
OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/
Install the "bun-runtime" agent skill from https://github.com/secondsky/claude-skills/tree/main/plugins/bun/skills/bun-runtime into .opencode/skills/bun-runtime/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "bun-runtime", then confirm the skill loads.OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
Facts
- Skill name
bun-runtime- GitHub stars
- 227
- Token cost
- ~1k tokens
- SKILL.md length
- 278 words
- Files
- 4 (incl. references)
- Skills in repo
- 169
- Repo updated
- First seen
- Licence
- MIT
At a glance
A skill your agent uses for Bun runtime, bunfig.toml, watch/hot modes, env vars, CLI flags, and module resolution.
- Watch/hot modes
- SKILL.md covers Quick Start, Core CLI Flags, Running Files and Package.json Scripts, plus 9 more sections
- Calls bun; needs API_KEY
- Module resolution
What it does
Bun Runtime is an agent skill from secondsky/claude-skills. Use for Bun runtime, bunfig.toml, watch/hot modes, env vars, CLI flags, and module resolution.
Its SKILL.md is about 1k tokens, which your agent loads only when the skill is triggered. The skill folder holds 4 other files, including reference files (for example `references/bunfig.md`, `references/cli-flags.md` and `references/module-resolution.md`).
It sits in Development. It works with Bun and Node.js. The repository describes itself as: Production-ready skills for Claude Code CLI - Cloudflare, React, Tailwind v4, and AI integrations. The licence is MIT.
When your agent uses it
- Watch/hot modes
- Module resolution
Example prompts
- “/bun-runtime”
Requirements
- Node.js
- A credential in API_KEY
What it can do on your machine
Read from SKILL.md and the folder at commit 8837836. It shows what the files ask for, not the result of running them.
Tool permissions
Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.
From allowed-tools in the SKILL.md frontmatter.
Runs code
Shell commands in SKILL.md call:
bun
From the folder's file list and the shell code blocks in SKILL.md.
Network
No URLs in SKILL.md.
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names these keys or tokens, usually read from environment variables:
API_KEY
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.
Context cost
Bun Runtime loads about 1k tokens when it runs, and up to ~5.2k if it reads all its reference files. Until then it costs about 27 tokens; SKILL.md has 278 words of instructions outside code blocks.
Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.
Safety
Auto-check: notes
The automated check noted patterns worth knowing about, such as sudo or a known installer.
- NoteMentions a .env fileSKILL.md:39
| `--env-file` | Load specific .env file | - NoteMentions a .env fileSKILL.md:92
Bun automatically loads `.env` files: - NoteMentions a .env fileSKILL.md:95
# Loads automatically: .env, .env.local, .env.development - NoteMentions a .env fileSKILL.md:99
bun --env-file .env.production run index.ts
Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.
SKILL.md
The full file from secondsky/claude-skills at commit 8837836, republished under its MIT licence (© secondsky). 278 words, ~1,038 tokens.
Download SKILL.mdSave it as
.claude/skills/bun-runtime/SKILL.md (or your agent's skills folder). This skill also uses 3 other files; get the full folder from GitHub.- name
- bun-runtime
- description
- Use for Bun runtime, bunfig.toml, watch/hot modes, env vars, CLI flags, and module resolution.
- metadata.version
- 1.0.0
- license
- MIT
Bun Runtime
Bun is a fast all-in-one JavaScript runtime built on JavaScriptCore (Safari's engine). It provides 4x faster startup than Node.js on Linux.
Quick Start
# Run a file
bun run index.ts
bun index.ts # shorthand
# Run with watch mode
bun --watch run index.ts
# Run package.json script
bun run dev
# Run with hot reloading
bun --hot run server.tsCore CLI Flags
| Flag | Purpose |
|---|---|
--watch | Restart on file changes |
--hot | Hot module replacement (preserves state) |
--smol | Reduce memory usage (slower GC) |
--inspect | Enable debugger |
--preload | Load modules before execution |
--env-file | Load specific .env file |
-e, --eval | Evaluate code string |
Running Files
Bun transpiles TypeScript and JSX on-the-fly:
bun run index.js
bun run index.ts
bun run index.jsx
bun run index.tsxImportant: Put Bun flags immediately after bun:
bun --watch run dev # Correct
bun run dev --watch # Wrong - flag passed to scriptPackage.json Scripts
# Run script
bun run dev
bun dev # shorthand (if no Bun command conflicts)
# List available scripts
bun run
# Run with Bun instead of Node
bun run --bun viteBun respects lifecycle hooks (preclean, postclean, etc.).
Watch Mode vs Hot Reloading
| Mode | Flag | Behavior |
|---|---|---|
| Watch | --watch | Full process restart on changes |
| Hot | --hot | Replace modules, preserve state |
# Watch mode - full restart
bun --watch run server.ts
# Hot reloading - preserves connections/state
bun --hot run server.tsEnvironment Variables
Bun automatically loads .env files:
# Loads automatically: .env, .env.local, .env.development
bun run index.ts
# Specify env file
bun --env-file .env.production run index.ts
# Disable auto-loading
# In bunfig.toml: env = falseAccess in code:
const apiKey = process.env.API_KEY;
const bunEnv = Bun.env.NODE_ENV;Globals Available
| Global | Source | Notes |
|---|---|---|
Bun | Bun | Main API object |
Buffer | Node.js | Binary data |
process | Node.js | Process info |
fetch | Web | HTTP requests |
Request/Response | Web | HTTP types |
WebSocket | Web | WebSocket client |
crypto | Web | Cryptography |
console | Web | Logging |
__dirname | Node.js | Current directory |
__filename | Node.js | Current file |
Preload Scripts
Load modules before your main script:
bun --preload ./setup.ts run index.tsOr in bunfig.toml:
preload = ["./setup.ts"]Use cases: polyfills, global setup, instrumentation.
Stdin Execution
# Pipe code to Bun
echo "console.log('Hello')" | bun run -
# Redirect file
bun run - < script.jsWorkspaces & Monorepos
# Run script in specific packages
bun run --filter 'pkg-*' build
# Run in all workspaces
bun run --filter '*' testDebugging
# Start debugger
bun --inspect run index.ts
# Wait for debugger connection
bun --inspect-wait run index.ts
# Break on first line
bun --inspect-brk run index.tsConnect via Chrome DevTools or VS Code.
Common Errors
| Error | Cause | Fix |
|---|---|---|
Cannot find module | Missing dependency | Run bun install |
Top-level await | Using await outside async | Wrap in async function or use .mts |
--watch not working | Flag in wrong position | Put flag before run |
When to Load References
Load references/bunfig.md when:
- Configuring bunfig.toml
- Setting up test configuration
- Configuring package manager behavior
- Setting JSX options
Load references/cli-flags.md when:
- Need complete CLI flag reference
- Configuring advanced runtime options
- Setting up debugging
Load references/module-resolution.md when:
- Troubleshooting import errors
- Configuring path aliases
- Understanding Bun's resolution algorithm
© secondsky, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file
Files
SKILL.md and 3 other files (references) in plugins/bun/skills/bun-runtime of secondsky/claude-skills.
- SKILL.md
- references/bunfig.md
- references/cli-flags.md
- references/module-resolution.md
Open the folder on GitHubat commit 8837836
Compare with similar skills
Bun Runtime next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.
| Skill | Stars | Used in | Tokens | Auto-check | Licence | Repo updated |
|---|---|---|---|---|---|---|
| Bun Runtime this skillsecondsky/claude-skills | 227 | — | ~1k | Automated safety check: Notes | MIT | |
| Bun Runtime and Toolkitmweinbach/agent-coworker | 156 | — | ~2.2k | Automated safety check: Notes | Custom licence | |
| Bungalfrevn/apollo | 237 | — | ~2k | Automated safety check: Notes | MIT | |
| Bunbastani-inc/atomic | 846 | — | ~2.8k | Automated safety check: Pass | Custom licence | |
| Electron Multi-Process ArchitectureiOfficeAI/AionUi | 33k | 1 repos | ~1.8k | Automated safety check: Pass | Apache-2.0 | |
| OpenTUI Terminal Interfacescline/cline | 70k | — | ~1.9k | Automated safety check: Pass | Apache-2.0 |
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Related
Categories
Questions about Bun Runtime
What does Bun Runtime do?
A skill your agent uses for Bun runtime, bunfig.toml, watch/hot modes, env vars, CLI flags, and module resolution. Bun Runtime is an agent skill from secondsky/claude-skills.toml, watch/hot modes, env vars, CLI flags, and module resolution.
When should I use Bun Runtime?
Bun Runtime fits situations like: watch/hot modes; module resolution.
How do I install Bun Runtime in Claude Code?
Run `npx skills add secondsky/claude-skills --skill bun-runtime -a claude-code`. Or copy the skill folder (plugins/bun/skills/bun-runtime in secondsky/claude-skills) into .claude/skills/bun-runtime in your project. Claude Code loads it when a task matches its description.
How do I install Bun Runtime in Codex?
Run `npx skills add secondsky/claude-skills --skill bun-runtime -a codex`. Or copy the skill folder (plugins/bun/skills/bun-runtime in secondsky/claude-skills) into .agents/skills/bun-runtime in your project. Codex loads it when a task matches its description.
Can I use Bun Runtime in Cursor, Gemini CLI or GitHub Copilot?
Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add secondsky/claude-skills --skill bun-runtime -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/bun-runtime, .gemini/skills/bun-runtime, .github/skills/bun-runtime and .opencode/skills/bun-runtime in your project.
What does Bun Runtime need to run?
Going by SKILL.md and its folder, Bun Runtime needs the command-line tools its instructions call (bun) and credentials named API_KEY. Our summary lists: Node.js; A credential in API_KEY.
Does Bun Runtime access the network?
SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.
Is Bun Runtime safe to install?
Our automated static check of SKILL.md found notes only (mentions a .env file), nothing it rates as a warning. It is not a guarantee. Review the folder before installing.
What licence does Bun Runtime use?
Bun Runtime is published under the MIT licence (declared in SKILL.md). It allows redistribution, so the full SKILL.md is shown on this page.
How many tokens does Bun Runtime use?
About 1k tokens (SKILL.md is roughly 4.2k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full. Its references folder adds about 4.1k tokens, read only when the agent opens those files.
What are the alternatives to Bun Runtime?
Skills that share tags, products or a category with Bun Runtime: Bun Runtime and Toolkit (mweinbach/agent-coworker, 156 stars), Bun (galfrevn/apollo, 237 stars), Bun (bastani-inc/atomic, 846 stars) and Electron Multi-Process Architecture (iOfficeAI/AionUi, 33k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.
Who maintains Bun Runtime?
secondsky (a GitHub user) maintains it in secondsky/claude-skills, which has 227 GitHub stars. The repository holds 169 skills in this directory. The repository was last updated on September 28, 2026.
Source: secondsky/claude-skills on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.