WebPerf Snippets

Measure Core Web Vitals and debug web performance with 56 snippets in a headless Chromium

Connector by nucliweb · GitHub account verified by the MCP Registry

IndexedMITLocal (stdio)★ 1,454

Install

Works with Claude Code, Codex, VS Code, Cursor, Windsurf, Claude Desktop. Read the repository before you give any tool access to your data.

npx agentmarket install connector/nucliweb-webperf-snippets

Asks which of your tools to add it to (Claude Code, Codex, Cursor, VS Code, Windsurf, Gemini CLI, Claude Desktop) and shows the change first. See https://agentmart.dev/cli.

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About

Measure Core Web Vitals and debug web performance with 56 snippets in a headless Chromium

Use cases: frontend-development, monitoring-observability

Reviews

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Permissions

What this server can do and what it asks for, from its tool list and install config. Checked Oct 25, 2026.

Tools: 6 read · 2 write · 0 delete
Secrets: 1 (API keys, tokens or passwords)
Install scripts: None found
Runs as: Node.js package

Tools by what they do 8

Read from the source code; the running server may list different tools.

Read 6 · Look things up without changing anything.

get_crux
list_snippets
open_page
read_results
run_snippet
run_workflow

Write 2 · Create, change, send or run things.

close_page
interact

Secrets and settings it asks for

Secrets: values you paste in that let it act as you.

CRUX_API_KEY

Tools (8)

Read from the source code; the running server may differ. Descriptions are the server’s own words; hidden characters are shown as [U+…].

close_pageClose a page
Closes a page opened with open_page. Closing a page that is already closed is not an error.
get_cruxGet CrUX field dataread-only
Returns the p75 of LCP, CLS and INP that real Chrome users had on a URL over the last 28 days, from the Chrome UX Report, with their rating. Falls back to the origin when the URL has no data of its own. Compare it with the lab values of run_snippet: field data is what users get.
interactInteract with an open page
Runs steps on a page opened with open_page, as a person would: click, type, hover, scroll or wait. A click or a key press is what the tracking snippets record. A step whose element does not appear within 5 seconds stops the run.
list_snippetsList snippetsread-only
Lists the web performance snippets this server can run, with their category, title and short aliases. Call it to find the name of the snippet to run.
open_pageOpen a pageread-only
Opens the URL in a headless Chromium that stays open between calls, and installs the snippets that record interactions (INP, Interactions, Input-Latency-Breakdown, and the other tracking snippets in list_snippets). Returns a sessionId for interact, read_results and close_page. At most 3 pages are open at a time, and a page closes after 10 minutes without use.
read_resultsRead the tracking snippetsread-only
Returns what the tracking snippets installed by open_page have recorded on the page so far, as the objects they return. A snippet with nothing recorded yet answers with status error, which is a result, not a failure.
run_snippetRun a snippetread-only
Opens the URL in a headless Chromium, runs one web performance snippet on the loaded page and returns the object the snippet returns, as defined in snippets/SCHEMA.md. Use list_snippets for the names. The snippets that record interactions (INP, Interactions, Input-Latency-Breakdown) run on a page opened with open_page instead.
run_workflowRun a workflowread-only
Opens the URL in a headless Chromium and runs a workflow: a sequence of snippets plus the follow-ups its decision tree adds from the results (for example LCP-Subparts when LCP is over 2.5 s, with the reason). core-web-vitals: LCP and CLS. audit: render-blocking resources, resource hints, critical CSS, TTFB, scripts, images and more. loading: TTFB, FCP, render-blocking, scripts and fonts. interaction: long tasks, animation frames, scroll and layout shifts while it scrolls the page.

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Stars: 1,454
Forks: 90
Open issues: 2
Last commit (this folder): Oct 24, 2026 (4 days ago)
Last release: Oct 25, 2026 (3 days ago)

From GitHub (fetched Oct 24, 2026).

Details

Registry name: io.github.nucliweb/webperf-snippets
Version: 1.5.0
Auth: API key
Packages: npm webperf-snippets
License: MIT
Repository: github.com/nucliweb/webperf-snippets
Website: webperf-snippets.net
First seen: Oct 24, 2026
Last checked: Oct 26, 2026
Source: Official MCP Registry github-graphql