Chromium Browser

Operate the configured Chrome DevTools MCP against the existing shared browser without disrupting unrelated tabs or authenticated state.

Environment Contract

• Treat ~/.local/libexec/mcp/chrome-devtools and the tools exposed in the current session as authoritative. The wrapper owns server versioning, flags, logging, and browser attachment; do not run the MCP package directly.
• The MCP attaches to an existing remote-debugging browser. Never launch a fallback browser or create another profile when attachment fails.
• Treat the browser as shared, authenticated, and concurrently used by the user and other agents. Inspect only pages relevant to the task and do not surface unrelated tab titles or content.
• Trust the live tool inventory; an absent tool is unavailable in this session. Do not advise editing client MCP configuration as a troubleshooting shortcut.

Reference Routing

For Wayback Machine capture discovery or replay research, read references/wayback-machine.md before making any Wayback request. Otherwise do not load it. Discover captures through serialized APIs outside Chromium, then open only the selected replay when rendered inspection adds evidence.

Page Ownership

1. Call list_pages before interacting and preserve the initial pages as pre-existing state.
2. Prefer new_page with background: true when a fresh page satisfies the task. Record the exact pageId returned by every page this task creates; never infer ownership from a later page-list difference.
3. Pass an explicit pageId to every page-scoped tool. Do not rely on selected-page state; use select_page only when deliberately bringing a page to the foreground.
4. Navigate or mutate a pre-existing page only when the task explicitly depends on that page's current state. Never close a pre-existing page.
5. At completion, close only the recorded pages created by this task unless the user asked to leave one open.

Interaction and Evidence

• On one page, navigate, wait for a useful known signal, take a fresh snapshot, then interact with identifiers from that snapshot. Refresh it after navigation or meaningful DOM changes.
• Prefer take_snapshot for structure and automation, take_screenshot for visual evidence, and evaluate_script for information absent from the accessibility tree. Accept wrapper screenshot defaults unless the task requires lossless or full-resolution output.
• Keep action responses small with includeSnapshot: false unless the updated state is immediately needed. Paginate and filter console, network, memory, and other high-volume results.
• When a cookie consent popup appears, select only necessary or essential cookies by default, including through its settings when needed. If no such option is available, accept all cookies and continue.
• Use filePath for large screenshots, snapshots, traces, recordings, or response bodies, writing only to a task-authorized workspace path or a temporary location. Unrestricted path capability is not write authorization.
• Parallelize independent pages when useful, but preserve causal order for calls targeting the same page.

Authority and Privacy

• Read-only inspection of task-relevant authenticated state is allowed when the task calls for it. Submitting forms, changing accounts, installing extensions, making purchases, or causing another external mutation requires the same authority that action would require outside the browser.
• Network-header redaction is an intentional server boundary. Do not bypass it or seek credentials through page or process introspection.

Troubleshooting

• On attachment or transport failure, distinguish the browser endpoint from the MCP process: check the debugging endpoint at http://127.0.0.1:${PRB_AGENT_CHROMIUM_PORT:-9222}/json/version, then inspect the newest per-process log under $XDG_CACHE_HOME/chrome-devtools-mcp/logs/ or, when unset, ~/.cache/chrome-devtools-mcp/logs/.
• Expect Chromium to remain healthy when an MCP transport drops. Report which layer failed and the supporting evidence; do not launch another browser, edit client configuration, or change wrapper flags unless the user explicitly requests configuration work.
• When a requested capability is missing, confirm the current tool inventory and wrapper configuration, then report the boundary. Do not invent a fallback that weakens the configured privacy or concurrency defaults.

Completion requires fresh tool evidence for the requested outcome and confirmation that task-created pages were either closed or intentionally left open.