coder/dev-server-sandbox
.mux/skills/dev-server-sandbox/SKILL.md
Run multiple isolated mux dev-server instances (temp MUX_ROOT + free ports)
$ install --global
skillsauthnpx skillsauth add coder/mux dev-server-sandboxInstall this skill globally with one command. Works with Claude Code, Cursor, and Windsurf.
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Last scanned: Apr 20, 2026, 8:35 AM41.7s1 file scanned
SKILL.md
- name:
- dev-server-sandbox
- description:
- Run multiple isolated mux dev-server instances (temp MUX_ROOT + free ports)
dev-server sandbox instances
make dev-server starts the mux backend server, which uses a lockfile at:
<MUX_ROOT>/server.lock(defaults to~/.mux-dev/server.lockin development)
This means you can only run one dev server per mux root directory.
This skill documents the repo workflow for starting multiple dev-server instances in parallel (including from different git worktrees) by giving each instance its own temporary MUX_ROOT.
Quick start
make dev-server-sandbox
What it does
- Creates a fresh temporary
MUX_ROOTdirectory - Copies these files into the sandbox if present (unless disabled by flags):
providers.jsonc(provider config)config.json(project list)
- Picks free ports (
BACKEND_PORT,VITE_PORT) - Disables tutorials by default inside the sandbox (
MUX_ENABLE_TUTORIALS_IN_SANDBOX=1opts back in) - Allows all hosts (
VITE_ALLOWED_HOSTS=all) so it works behind port-forwarding domains - Runs
make dev-serverwith those env overrides
Options
# Start with a clean instance (do not copy providers or projects)
make dev-server-sandbox DEV_SERVER_SANDBOX_ARGS="--clean-providers --clean-projects"
# Skip copying providers.jsonc
make dev-server-sandbox DEV_SERVER_SANDBOX_ARGS="--clean-providers"
# Clear projects from config.json (preserves other config)
make dev-server-sandbox DEV_SERVER_SANDBOX_ARGS="--clean-projects"
# Use a specific root to seed from (defaults to ~/.mux-dev then ~/.mux)
SEED_MUX_ROOT=~/.mux-dev make dev-server-sandbox
# Keep the sandbox root directory after exit (useful for debugging)
KEEP_SANDBOX=1 make dev-server-sandbox
# Pin ports (must be different)
BACKEND_PORT=3001 VITE_PORT=5174 make dev-server-sandbox
# Re-enable tutorials for sandbox dogfooding
MUX_ENABLE_TUTORIALS_IN_SANDBOX=1 make dev-server-sandbox
# Override which make binary to use
MAKE=gmake make dev-server-sandbox
Security notes
providers.jsoncmay contain API keys.- The sandbox root directory is created on disk (usually under your system temp dir).
- This flow intentionally does not copy
secrets.json.
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