Browser Lanes Claude Code mod: share one Claude Code Playwright browser

Browser Lanes is a community mod by Hamza Zafar (hamzafer), part of his claude-code-mods collection. It is for people who give Claude Code a Playwright browser through the Playwright MCP server, and who run several sessions or subagents at once. The Claude Code Playwright browser is a single Chrome with a single profile, and two things trying to drive it at the same time is where the "Browser is already in use" error comes from.

The mod adds a line above the prompt: ◎ browser: followed by the state of this session. It reads attached · this session's Chrome, ready · browser not open yet, or, in red, NOT attached · another Claude (pid …) holds the shared profile. When something is using the browser, the line adds driving: <name> and, if others are queued, 2 waiting (main, login-test). If the session has no Playwright server, nothing is drawn.

Three other behaviors come with it, according to the author's code comments:

• Within one session, the main agent and each subagent take turns. A second driver's browser call waits until the first has closed the browser, finished its turn, or been idle for 90 seconds.
• Screenshots are named by who took them, such as main-01.png or login-test-03.png, and a filename you asked for gets the driver's name in front.
• If another Claude session used the browser in the last 90 seconds, you get a toast.

/browser explains the current state, and /browser clean lists the Playwright browsers that belong to other Claude sessions and lets you close them.

Use any of the methods in the install block; they install straight from the author's own marketplace. You also need the Playwright MCP server set up in Claude Code, since the mod only watches and coordinates it. Restart Claude Code or run /reload-plugins after installing.

The mod is one hooks module, hooks/register.tsx, plus a process-list parser in hooks/attach.ts. It hooks tool.call and acts only on tools whose name matches mcp__*playwright*__browser_. Everything else passes straight through. For those tools it reads who holds the lane, waits if someone else does, records itself as the holder, optionally renames the screenshot file, and then calls the real tool.

To work out whose Chrome is whose, it runs ps -axo pid=,ppid=,command= and walks parent processes: Claude, then npm exec @playwright/mcp, then playwright-mcp, then Chrome with --user-data-dir=. When it has to close a browser, it checks again that the pid is still a Playwright Chrome before sending kill:

async function closeChrome($: EngineInterface, pid: number) {
  const now = await $.process.run(['ps', '-p', String(pid), '-o', 'command='], { timeoutMs: 2_000 }).catch(() => null)
  if (!now || now.exitCode !== 0 || !/--user-data-dir=/.test(now.stdout) || /Helper/.test(now.stdout)) return false
  const r = await $.process.run(['kill', String(pid)], { timeoutMs: 2_000 }).catch(() => null)
  return r?.exitCode === 0
}

If a browser call fails with "already in use", the mod asks whether to close the blocking browser and, on yes, retries once. The holder, the waiting list and the attachment live in host-held state so they survive a reload. A small record of the last driver (session id, name, time) goes in the plugin's store, which is how one session notices another.

There are no options in /config. The mod follows the band order file that the author's claude-code-mods checklist writes, at <config dir>/claude-code-mods/bands.json, so you can decide whether this band sits above or below other band mods. It reads that file once per session, so restart to apply a change. The 90-second idle limit and the 5-minute wait limit are constants at the top of register.tsx. To stop the queueing and screenshot renaming entirely, run Playwright with --isolated and disable the plugin with /plugin disable browser-lanes.

We read every file the plugin can execute before running it: hooks/hooks.json, register.tsx, attach.ts, bands.ts, the type declarations and the tests. There is no package.json, install script, bundled code or binary. The repository has a root LICENSE (MIT, Hamza Zafar). Here is what we found:

• Network: none.
• Runs commands ($.process.run): sh -c 'echo $PPID' to find the Claude process, ps -axo pid=,ppid=,command=, lsof -a -p <pid> -d cwd -Fn for other Claude processes with a Playwright Chrome, ps -p <pid> -o command=, sleep (0.5 s while waiting, 1.5 s before a retry), and kill <pid>. Each call is an argv array, not a shell string, apart from the fixed sh -c one. The process list stays on your machine.
• Closes processes: kill is sent to a Chrome whose command line still contains --user-data-dir= and is not a Helper. For other sessions' browsers it happens only after you choose in a prompt (/browser clean, or after an "already in use" error). It does close this session's own Chrome when the session ends, without asking. Claude sessions themselves are never killed.
• Blocks tool calls: the tool.call hook can make a Playwright call wait, and after 5 minutes it refuses the call with a message. It also changes the filename of screenshots. These match the README. Validate notes that the tool.call and agent.spawn hooks have no .catch.
• Files: it only reads, namely <config dir>/claude-code-mods/bands.json through $.fs.read. It writes nothing outside the plugin's store and host state. It reads the CLAUDE_CONFIG_DIR and HOME environment variables.
• No daemons, secrets or telemetry, and no text is injected into prompts or tool results. The only message aimed at the model is the refusal after a 5-minute wait.
• Requirements: the Playwright MCP server and Chrome or Chromium. On macOS or Linux, ps, lsof and kill must be available.

claude plugin validate reported no errors or warnings for the plugin; its directory check only noted that no icon is provided. The author's 11 tests all passed on Claude Code 2.1.307.

Checked with Claude Code 2.1.307 on macOS (validate and tests). We did not drive a real Playwright browser, so the process matching is verified only by the author's tests. If the band does not show:

• No band means the session has no Playwright server. Run /browser; it should print no Playwright server in this session.
• The mod recognizes servers by playwright-mcp or mcp-server-playwright in the process command. A differently named server will not be found.
• The band hides while a survey is open above the prompt.
• If /browser is refused because Claude Code already has a command of that name, the mod still runs but the command is missing.

For the red "NOT attached" state, run Playwright with --isolated, or use /browser clean.