# Cmux > Manage cloud development sandboxes with cmux. Create, sync, and access remote VMs. Includes browser automation via Chrome CDP for scraping, testing, and web interaction. Use when this capability is needed. - Skill: `tomevault-io/cmux-2` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/cmux-2` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/cmux-2/raw - Safety review: pending (external: skill-scanner PASS, skillspector PASS) - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: DevOps & Infra - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/cmux-2 --- # cmux - Cloud Sandboxes for Development cmux manages cloud sandboxes for development. Use these commands to create, manage, and access remote development environments with built-in browser automation. ## Installation ```bash npm install -g cmux ``` ## Quick Start ```bash cmux login # Authenticate (opens browser) cmux start ./my-project # Create sandbox, upload directory → returns ID cmux start . # Or use current directory cmux code # Open VS Code cmux pty # Open terminal session cmux upload ./my-project # Upload files/directories to sandbox cmux download ./output # Download files from sandbox cmux computer screenshot # Take browser screenshot cmux stop # Stop sandbox cmux delete # Delete sandbox cmux ls # List all sandboxes ``` > **Preferred:** Always use `cmux start .` or `cmux start ` to sync your local directory to a cloud sandbox. This is the recommended workflow over cloning from a git repo. ## Commands ### Authentication ```bash cmux login # Login (opens browser) cmux logout # Logout and clear credentials cmux whoami # Show current user and team ``` ### Sandbox Lifecycle ```bash # Preferred: local-to-cloud (syncs your local directory to the sandbox) cmux start . # Create sandbox from current directory (recommended) cmux start ./my-project # Create sandbox from a specific local directory cmux start -o . # Create from local dir and open VS Code immediately # Alternative: clone from git cmux start --git user/repo # Clone a git repo into sandbox cmux start --docker # Create sandbox with Docker support cmux ls # List all sandboxes cmux status # Show sandbox details and URLs cmux stop # Stop sandbox cmux extend # Extend sandbox timeout cmux delete # Delete sandbox permanently cmux templates # List available templates ``` ### Access Sandbox ```bash cmux code # Open VS Code in browser cmux vnc # Open VNC desktop in browser cmux pty # Interactive terminal session ``` ### Work with Sandbox ```bash cmux pty # Interactive terminal session (use this to run commands) cmux exec # Execute a one-off command ``` > **Important:** Prefer `cmux pty` for interactive work. Use `cmux exec` only for quick one-off commands. ### File Transfer Upload and download files or directories between local machine and sandbox. ```bash # Upload (local → sandbox) cmux upload # Upload current dir to /home/user/workspace cmux upload ./my-project # Upload directory to workspace cmux upload ./config.json # Upload single file to workspace cmux upload . -r /home/user/app # Upload to specific remote path cmux upload . --watch # Watch and re-upload on changes cmux upload . --delete # Delete remote files not present locally cmux upload . -e "*.log" # Exclude patterns # Download (sandbox → local) cmux download # Download workspace to current dir cmux download ./output # Download workspace to ./output cmux download . -r /home/user/app # Download from specific remote path ``` ### Browser Automation (cmux computer) Control Chrome browser via CDP in the sandbox's VNC desktop. #### Navigation ```bash cmux computer open # Navigate to URL cmux computer back # Navigate back cmux computer forward # Navigate forward cmux computer reload # Reload page cmux computer url # Get current URL cmux computer title # Get page title ``` #### Inspect Page ```bash cmux computer snapshot # Get accessibility tree with element refs (@e1, @e2...) cmux computer screenshot # Take screenshot (base64 to stdout) cmux computer screenshot out.png # Save screenshot to file ``` #### Interact with Elements ```bash cmux computer click # Click element (@e1 or CSS selector) cmux computer type "text" # Type into focused element cmux computer fill "value" # Clear input and fill with value cmux computer press # Press key (Enter, Tab, Escape, etc.) cmux computer hover # Hover over element cmux computer scroll [direction] # Scroll page (up/down/left/right) cmux computer wait # Wait for element to appear ``` #### Element Selectors Two ways to select elements: - **Element refs** from snapshot: `@e1`, `@e2`, `@e3`... - **CSS selectors**: `#id`, `.class`, `button[type="submit"]` ## Sandbox IDs Sandbox IDs look like `cmux_abc12345`. Use the full ID when running commands. Get IDs from `cmux ls` or `cmux start` output. ## Common Workflows ### Create and develop in a sandbox (preferred: local-to-cloud) ```bash cmux start ./my-project # Creates sandbox, uploads files cmux code cmux_abc123 # Open VS Code cmux pty cmux_abc123 # Open terminal to run commands (e.g. npm install && npm run dev) ``` ### File transfer workflow ```bash cmux upload cmux_abc123 ./my-project # Push local files to sandbox # ... do work in sandbox ... cmux download cmux_abc123 ./output # Pull files from sandbox to local ``` ### Browser automation: Login to a website ```bash cmux computer open cmux_abc123 "https://example.com/login" cmux computer snapshot cmux_abc123 # Output: @e1 [input] Email, @e2 [input] Password, @e3 [button] Sign In cmux computer fill cmux_abc123 @e1 "user@example.com" cmux computer fill cmux_abc123 @e2 "password123" cmux computer click cmux_abc123 @e3 cmux computer screenshot cmux_abc123 result.png ``` ### Browser automation: Scrape data ```bash cmux computer open cmux_abc123 "https://example.com/data" cmux computer snapshot cmux_abc123 # Get structured accessibility tree cmux computer screenshot cmux_abc123 # Visual capture ``` ### Clean up ```bash cmux stop cmux_abc123 # Stop (can restart later) cmux delete cmux_abc123 # Delete permanently ``` ## Security: Dev Server URLs **CRITICAL: NEVER share or output raw E2B port-forwarded URLs.** When a dev server runs in the sandbox (e.g., Vite on port 5173, Next.js on port 3000), E2B creates publicly accessible URLs like `https://5173-xxx.e2b.app`. These URLs have **NO authentication** — anyone with the link can access the running application. **Rules:** - **NEVER** output URLs like `https://5173-xxx.e2b.app`, `https://3000-xxx.e2b.app`, or any `https://-xxx.e2b.app` URL - **NEVER** construct or guess E2B port URLs from sandbox metadata - **ALWAYS** tell the user to view dev servers through VNC: `cmux vnc ` - VNC is protected by token authentication (`?tkn=`) and is the only safe way to view dev server output - Only VSCode URLs (`cmux code `) and VNC URLs (`cmux vnc `) should be shared — these have proper token auth **When a dev server is started:** ``` ✓ Dev server running on port 5173 View it in your sandbox's VNC desktop: cmux vnc (The browser inside VNC can access http://localhost:5173) ``` **NEVER do this:** ``` Frontend: https://5173-xxx.e2b.app ← WRONG: publicly accessible, no auth ``` ## Tips - Run `cmux login` first if not authenticated - Use `--json` flag for machine-readable output - Use `-t ` to override default team - Use `-v` for verbose output - Always run `snapshot` first to see available elements before browser automation - Use element refs (`@e1`) for reliability over CSS selectors --- > Converted and distributed by [TomeVault](https://tomevault.io/claim/manaflow-ai) — claim your Tome and manage your conversions.