Chromium Browser

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

This skill owns rendered browser UI interaction, inspection, automation, and verification through shared Chromium. Use search, fetch, APIs, CLIs, or connectors for retrieval when they fit, and host native-app tools for non-browser UI. Do not use native-app tools as a fallback around this skill's shared-browser attachment, page-ownership, or privacy rules. If the user selects another available browser integration, follow its tool contract without mixing controllers.

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

Call list_pages before interacting and preserve the initial pages as pre-existing state.
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.
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 or recovering the closed-page context described below.
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.
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

If closing an owned page returns The selected page has been closed and list_pages repeats it, the close may have succeeded while MCP retained a stale selection. Select a previously observed surviving page with bringToFront: false, then call list_pages and confirm the owned page ID is absent. This recovery attempts only to repair MCP context: do not navigate, inspect, or close the surviving page, and suppress unrelated titles and content from results. Do not repeat the close or create another tab to recover selection.
If select_page also returns the same closed-page error, stop MCP recovery attempts and report the stale session context. A read-only /json/list request at the configured debugging endpoint can confirm that a task page's known, unique, unchanged URL is absent; filter locally and return only that result, never unrelated targets. This is closure evidence, not MCP recovery or authorization to control the browser through another route. MCP pageId values are not CDP target IDs. If the owned page cannot be identified reliably, report cleanup as unverified; do not infer ownership from the endpoint list or use it to close tabs.
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/.
A responsive endpoint proves the browser process is alive, not that renderers can start. If new_page times out and tabs show a crashed icon or Untitled, stop repeated creation attempts and check browser health separately from MCP transport health. A failed creation can leave a tab without returning a pageId; do not infer ownership from a later page list or close unidentified tabs.
After a macOS Homebrew Chromium upgrade, compare the endpoint's Browser version with plutil -extract CFBundleShortVersionString raw /Applications/Chromium.app/Contents/Info.plist. Confirm the running process uses that app bundle and inspect its start time and versioned framework/helper paths. Homebrew can replace the bundle while the old process keeps running, removing helpers it needs for new renderers; existing pages and /json/version can still work. A version mismatch alone is a clue, not proof of the failure.
Report the failed layer and evidence. Do not change client configuration or wrapper flags without authorization for that configuration work. Do not automatically restart the shared browser during ordinary browsing or from the wrapper. An explicit request to repair the browser authorizes a graceful restart using the same profile and debugging port. Record those arguments first and preserve the session; chrome://restart requests a session-restoring restart. If the old process exits but cannot relaunch after an upgrade, confirm it has exited, then reopen the installed executable with the recorded profile/port arguments and --restore-last-session, never a fallback profile. Respect any unsaved-work prompt. Recheck the live version, call list_pages for fresh IDs, verify pre-existing pages were restored, and test creation and navigation on an owned page before closing it.
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.

chromium-browser