# Localhost Radar

> Localhost Radar is a free Chrome extension by Slow Signal Labs. It lists every server listening on your own computer, says which AI coding tool started each one (Claude Code, Codex, Antigravity, Gemini CLI, Cursor and others) and how sure it is, groups a project's servers together, and lets you open them or stop them safely. Everything runs on your computer: no account, no analytics, no remote servers.

Version 0.1.0, released 2 November 2026. The Chrome Web Store listing is in review. It works in Chrome, Edge, Brave, Arc, Vivaldi and Chromium (version 120 or later) on macOS, Linux and Windows. Its helper needs Python 3.8 or later.

**The problem it solves.** Coding agents start servers: a dev server, a preview of the build, Storybook, a second copy in a git worktree. They often leave them running. An hour later a port is taken and nobody remembers which agent started what. Radar answers "what is running on localhost, who started it, is it still answering, and can I stop it safely?"

**How it works.** A browser cannot see which program owns a port, so Radar ships with a small helper: a readable Python script that the extension's setup page generates and that you install with one command, without admin rights.
- It installs to `~/.localhost-radar` on macOS and Linux, or `%LOCALAPPDATA%\LocalhostRadar` on Windows, and is registered as the Chrome native-messaging host `com.localhost_radar.helper`.
- The browser starts it only when Radar asks, and only this extension may start it.
- It reads the list of listening TCP ports and, for your own processes, their command line, working folder, parent processes, start time, CPU and memory.
- Without the helper, Radar still finds servers on common ports, but cannot say who started them or stop them.

**How it decides who started a server.** It walks up the parent processes from the listening process, and the nearest AI tool counts as the starter. It reports one of three levels of certainty, with the reason:
- **Sure:** the server was started inside that tool's session.
- **Likely:** only an environment marker the tool leaves in child processes remains, for example because the server was detached; or the server was started from an AI editor's terminal, where you may have typed the command yourself; or the program only shares a common name with the tool.
- **Guess, or no AI tool:** stated as such.

**Tools it recognises.**
- Claude Code and the Claude app
- Codex CLI and the ChatGPT / Codex app
- Antigravity, Antigravity IDE and its `agy` CLI
- Gemini CLI, Cursor, GitHub Copilot CLI, OpenCode, Amp, Aider, Qwen Code, Goose, Crush, Kiro, Cline, Factory Droid, Kimi Code, Mistral Vibe, Grok Build, Junie, Auggie (Augment) and Qoder
- the Windsurf, Trae, Qoder and CodeBuddy editors

Agents that run as VS Code extensions show as started from VS Code. Cloud agents do not run servers on your computer.

**What it shows for each server.**
- the port, the project (from `package.json`, `pyproject.toml` and similar), the git branch and worktree
- a role (dev, preview, Storybook, docs, tests, API, static) and the reason for it
- HTTP status, page title and icon
- uptime, CPU and memory
- which open tabs already point at it

Servers of one git repository are grouped into a stack, including worktrees and monorepo packages, even when different agents started them.

**What it flags.**
- servers whose agent session has ended ("detached")
- servers reachable from other devices on the network
- two programs on one port (IPv4 versus IPv6)
- servers that hang or return 5xx errors
- ports Chrome refuses to open
- tabs whose server is gone

**How stopping works.**
- Radar first shows exactly what will end, including the runner, watcher or reloader that would restart the server and other ports that stop with it, and anything in that tree it will leave running.
- Before sending the normal shutdown signal, it checks that the process is still the same one you saw.
- It forces a stop only if you ask.
- It never stops your shell, terminal, editor, the AI tool itself, Docker, the browser Radar runs in, or an AI tool's own internal ports.

**Using it.**
- It works as a toolbar popup, in the side panel, or in a full tab. Alt+Shift+L opens the popup and Alt+Shift+K the full view.
- Servers can be renamed, pinned or hidden, and you can correct who started one. These settings stay in the browser.
- Notifications are optional.
- The helper also works as a command-line tool: `~/.localhost-radar/run.sh --table`, or `--json`, or `--all` to include system services.

**Install.**
1. Add the extension to the browser.
2. Its setup page opens and generates a helper installer for this copy of Radar.
3. Run `bash ~/Downloads/install-localhost-radar.sh` on macOS or Linux. On Windows, run `powershell -ExecutionPolicy Bypass -File "$env:USERPROFILE\Downloads\install-localhost-radar.ps1"`.

The setup page turns green when the helper answers. Remove the helper with `--uninstall` (`-Uninstall` on Windows).

**Privacy.**
- Radar collects and sends nothing. It talks only to its helper and to servers on localhost.
- Extension permissions: `nativeMessaging`, `alarms`, `storage`, `sidePanel`, and optionally `notifications`. Host access is limited to `localhost`, `127.0.0.1`, `[::1]` and `*.localhost`.
- Your names, pins and one day of history stay in browser storage on this device.

## Docs

- [Localhost Radar, the full page](https://radar.slowsignal.xyz/index.md): what it shows, stacks, flags, stopping, the tools it recognises, how it works, and install steps.
- [Privacy policy](https://radar.slowsignal.xyz/privacy.md): exactly what it reads on your computer, what it stores, what it sends (nothing) and what it changes.

## Optional

- [Website](https://radar.slowsignal.xyz/): the same page with screenshots, in English, Japanese, Korean, and Simplified and Traditional Chinese.
- [Slow Signal Labs](https://slowsignal.xyz): the independent studio that makes Localhost Radar.