LeftOpen – Native macOS menu bar app to see what's on localhost and close it

Developer SonghaiFan released LeftOpen, a native macOS menu bar app and bundled CLI that lists listening localhost ports, identifies the owning process and project, and closes selected ports with SIGTERM only. LeftOpen runs on macOS Sonoma 14.0+ as a universal binary for Apple Silicon and Intel Macs, is signed with a Developer ID and notarized by Apple, and installs via `brew install --cask songhaifan/tap/leftopen` or a GitHub Releases zip. The app distinguishes 127.0.0.1 from 0.0.0.0 bindings, groups ports by origin (dev servers, launchd services, apps, system), and ships a `leftopen` CLI with identical inference and safety rules.

Native macOS Menu Bar Port Manager & CLI See what your tools left running on localhost, identify projects, and gently close them. 把那些虚掩着的门，轻轻关上。 English · 中文 https://github.com/SonghaiFan/leftopen/blob/main/README.zh-CN.md When I have several coding agents working in parallel, dev servers and test runners keep starting up on different ports. By the end of the day there are always a few still running. Existing tools are either too much, or only tell you "port in use" without saying which process it is or which project it came from. So I made LeftOpen . It sits quietly in the menu bar and shows you the listening ports, the processes behind them and the projects they probably belong to. Once you've had a look, you close the ones you no longer need. Close the doors that were left ajar, gently. brew install --cask songhaifan/tap/leftopen Supports Apple Silicon and Intel Macs running macOS Sonoma 14.0+ . The app and bundled CLI are universal binaries, signed with a Developer ID and notarized by Apple. Get LeftOpen-release.zip from GitHub Releases https://github.com/SonghaiFan/leftopen/releases/latest , unzip, and move LeftOpen.app to /Applications . - Knows whose port it is. Walks up from the process's working directory to .git , package.json , pyproject.toml , Cargo.toml or go.mod , or resolves the owning .app . Global npm packages, python -m modules and standalone services Redis, Postgres, Ollama… are named too, so you rarely see a bare node or python . - Real icons, nothing bundled. Uses the .app icon when there is one; otherwise the icon the project or package ships itself Tauri/Electron app icon, the favicon declared in index.html , public/ conventions ; otherwise the favicon served by the local server; otherwise a symbol. - Grouped by who started them. Dev Servers from a project, terminal, editor or agent , Background Services launchd: brew services, login items , Apps and System. The group is also how a port is closed for good, and each one says so: SIGTERM for dev servers, brew services stop … for services launchd would restart, quitting the app for apps. - Closes gently. Shows the process's other ports before you confirm, re-checks PID and start time at the moment of closing, sends SIGTERM only. Never SIGKILL , never system processes. - Local vs LAN. Tells apart ports bound to 127.0.0.1 from ones on 0.0.0.0 or a LAN address. - Nothing running in the background. Native SwiftUI MenuBarExtra . No daemon, no Dock icon, no telemetry. The only request that leaves this Mac is a daily check of the latest GitHub release, which you can turn off in Settings. - Same engine in the terminal. The app ships a leftopen CLI with identical inference and safety rules. - Fix "Port already in use" EADDRINUSE : When your dev server fails because port 3000, 5173, or 8080 is blocked by a lingering process, LeftOpen shows you what's running and shuts it down gently—without restarting your terminal or machine. - Identify the project, not just a generic node or python PID : Tools like lsof -i or kill-port only report raw PIDs or ambiguous process names. LeftOpen tracks the working directory and project root package.json , Cargo.toml , pyproject.toml , go.mod , .git , giving you full context before taking action. - Spot accidental LAN exposure : See at a glance whether a port is bound strictly to 127.0.0.1 local only or 0.0.0.0 accessible to anyone on your local network/Wi-Fi . - Graceful SIGTERM vs. destructive kill -9 : Unlike blunt force-killing scripts, LeftOpen re-verifies PID and start time, shows sibling ports, and issues a standard SIGTERM so servers can clean up sockets, flush logs, and exit cleanly. Available in the terminal right after installing: List every listening port and its owner or: leftopen list leftopen Explain one port leftopen 3000 Open http://localhost:3000 in the default browser leftopen open 3000 Close the process on a port SIGTERM, asks first leftopen close 3000 Structured JSON output leftopen --json Sample output: LEFT OPEN 26 listening ports · 17 processes · 1 projects · 8 LAN-visible MY PROJECTS 2 PORT PID OWNER PROCESS AGE SCOPE 5173 76344 visdelta node 2h LOCAL ↳ ~/Documents/visdelta 5511 4999 visdelta node 27m LOCAL ↳ ~/Documents/visdelta APPLICATIONS 16 PORT PID OWNER PROCESS AGE SCOPE 5000 696 ControlCenter Control 3d LAN 9222 36824 Google Chrome Chrome 5h LOCAL SERVICES 3 PORT PID OWNER PROCESS AGE SCOPE 11434 911 Ollama ollama 1d LOCAL LOCAL = this Mac only · LAN = may be reachable from your local network Tests swift test Build the app locally LEFTOPEN OUTPUT DIR=dist/dev Scripts/build-app.sh