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Browser Agent / Shared browser

browser already in use

A previous agent session or shared MCP server still owns the browser handle.

Error text / 报错原文

  • browser already in use
  • Browser is already in use
  • another session is using the browser

What it means

A previous agent session or shared MCP server still owns the browser handle.

Most common causes

  • Parallel agents share one browser
  • Stale process did not release CDP connection
  • Hosted browser pool has not recycled the session
  • User opened the same debugging profile manually

Fastest fix

  • Reproduce the smallest failing case outside the agent.
  • Confirm auth, session, and transport before changing app code.
  • Disable unrelated tools or servers and retry once.
  • Capture the exact timestamp, client version, and raw error text.

Safe fix

  • Keep secrets in environment variables or the platform secret store.
  • Use least-privilege scopes and read-only tools by default.
  • Add validation around manifests, schemas, and callback URLs.
  • Document the working local and production configuration.

What not to do

  • Do not paste OAuth tokens or session IDs into public logs.
  • Do not bypass TLS, CSP, or permission prompts as a permanent fix.
  • Do not enable every MCP tool globally just to make one task pass.

Diagnostic commands

node --version
npx @playwright/mcp@latest --help
curl http://127.0.0.1:9222/json/version

Related tools

Related errors

Sources