WebPerf Snippets MCP Server: Setup for Claude, Cursor and Other Apps

• Measures one performance metric on a web page

  Opens a page in a hidden Chromium browser, runs one tested measurement such as LCP or TTFB, and returns the result as structured data. Interaction-based snippets need open_page instead.

  Try: “Run the LCP-Subparts snippet on https://example.com on a mobile screen.”

  Network · run_snippet

• Runs a set of related measurements and follows up on problems

  Runs a chain of snippets for core web vitals, loading, interaction or a full audit, and adds follow-up snippets when a result looks poor, such as a slow LCP.

  Try: “Do a full performance audit of https://example.com.”

  Network · run_workflow

• Lists the available measurements

  Returns the names, categories and short aliases of the performance snippets the server can run, so the assistant can pick the right one.

  Try: “Which snippets can you run for images?”

  Read · list_snippets

• Gets real-user speed data for a page from Chrome's UX report

  Fetches the 75th percentile LCP, CLS and INP that real Chrome users had over 28 days, with an optional weekly trend. It needs a free Chrome UX Report API key set on the server.

  Try: “What do real users see for LCP on https://example.com on phones, with a 12-week trend?”

  Network · get_crux

• Opens a page that stays open so interactions can be recorded

  Starts a hidden browser page and installs the snippets that record interactions. At most 3 pages stay open, and one closes after 10 minutes without use.

  Try: “Open https://example.com and track INP so I can test the menu.”

  Network · open_page

• Clicks, types, hovers and scrolls on an open page

  Runs up to 50 steps on a page you opened, such as click, type, hover, scroll and wait. A click can submit a form or change data on the site, so it is not read-only.

  Try: “On the open page, click the Menu button, then scroll down 600 pixels.”

  Write · interact

• Reads what the tracking snippets recorded

  Returns what the interaction snippets recorded on an open page so far, such as INP after you clicked around.

  Try: “What did the tracking snippets record after those clicks?”

  Read · read_results

• Shows the full result behind a summary

  Large results come back as summaries. This returns the whole object for one snippet of that run without measuring again.

  Try: “Show me the full details of the LCP result from the last run.”

  Read · get_details

• Closes an open page

  Closes a page opened earlier. Closing a page that is already closed is not an error.

  Try: “Close the page you opened.”

  Write · close_page

Watch out for

• One tool can click and type on pages

  The interact tool runs click, type and scroll steps, and the source says a click can submit a form or change data on the site. The browser starts clean with no logins, but do not point it at sites where you want nothing changed. github.com

• Page content comes back to the assistant

  Selectors, URLs and alt texts from the measured page are returned to the assistant. The server tells the assistant to treat them as data, not instructions, but a hostile page could still try to steer it. github.com

• It can open local and private addresses

  The URL check only requires http or https, and the tool description says local dev servers work. Measure only addresses you mean to. github.com

Security advisories