LightScout MCP

Part of the TestScout MCP Suite — AI-powered QA tools for modern development teams.

Core Web Vitals analysis powered by Lighthouse. Runs as an MCP server for AI coding tools (Claude Code, Cursor, Windsurf, etc.) or as a standalone CLI for CI pipelines and terminals. Four tools: analyze a URL, compare two URLs, check against thresholds, or crawl an entire site.

Requirements

• Node.js >= 18
• Google Chrome or Chromium

MCP Server Setup

Claude Code

claude mcp add lightscout -- npx -y lightscout-mcp

Cursor, VS Code, Windsurf, Cline, Roo Code, Gemini CLI

All use the same mcpServers JSON format. Add this to the appropriate config file:

{
  "mcpServers": {
    "lightscout": {
      "command": "npx",
      "args": ["-y", "lightscout-mcp"]
    }
  }
}

Zed

Zed uses context_servers instead of mcpServers:

{
  "context_servers": {
    "lightscout": {
      "command": "npx",
      "args": ["-y", "lightscout-mcp"]
    }
  }
}

CLI

Install

npm install -g lightscout-mcp

Try without installing

npx -p lightscout-mcp lightscout analyze https://example.com

Commands

lightscout analyze <url> [--device mobile|desktop] [--categories perf,a11y,seo,best-practices]
lightscout compare <urlA> [urlB] [--device mobile|desktop]
lightscout crawl <url> [--max-pages N] [--device mobile|desktop]
lightscout check <url> [--perf 90] [--lcp 2500] [--fcp 3000] [--cls 0.1] [--tbt 300] [--ttfb 1800]

Examples

Analyze a single page:

lightscout analyze https://example.com
lightscout analyze https://example.com --device desktop --categories performance,accessibility

Compare two URLs, or the same URL on mobile vs desktop:

lightscout compare https://a.com https://b.com
lightscout compare https://example.com                    # mobile vs desktop

Crawl a site and audit discovered pages:

lightscout crawl https://example.com --max-pages 5

CI quality gate (exits 1 on failure):

lightscout check https://example.com --perf 90 --lcp 2500

Tools

analyze_performance

Run Lighthouse on a URL. Returns performance scores, Core Web Vitals (LCP, FCP, CLS, TBT, SI, TTFB) with good/needs-improvement/poor ratings, top recommendations sorted by impact, and diagnostics.

compare_performance

Compare Core Web Vitals between two URLs, or the same URL on mobile vs desktop. Shows per-metric deltas with winner indicators.

check_threshold

Pass/fail check against performance thresholds. Useful for CI quality gates.

Default thresholds use Google's "poor" boundary -- only fails if metrics are genuinely bad:

crawl_site

Discover pages on a site (via sitemap.xml or link crawling) and run Lighthouse on each. Returns per-page results plus site-wide summary with avg/min/max scores and common issues.

Pages are discovered via sitemap.xml first, falling back to link crawling. Up to 3 Lighthouse runs execute in parallel.

CWV Rating Thresholds

Notes

• TBT (Total Blocking Time) is used instead of INP/FID because Lighthouse runs lab-only tests with no real user interaction.
• Up to 3 concurrent Lighthouse runs (semaphore-controlled).
• Chrome is launched headless and killed after each audit.
• MCP responses are token-optimized with condensed metrics and compact JSON.

TestScout MCP Suite

LightScout is the first tool in the TestScout MCP Suite. More tools are coming:

Follow development at testscout.dev.

License

MIT