How to Identify Render-Blocking Resources with Claude
Find render-blocking CSS and JS with Claude and ToolRouter. Speed up first paint with targeted fixes.
Tool
Claude identifies render-blocking CSS and JavaScript, then explains the impact of each resource on your page's first paint time. Ask for specific fixes like inline critical CSS strategies, async loading patterns, or font optimization techniques, and get actionable code suggestions tailored to your tech stack.
Connect ToolRouter to Claude
1Go to Settings → Connectors → Add custom connector
2Enter the details below and click Add
Name
ToolRouterURL
https://api.toolrouter.com/mcp3Done — works on Claude chat, desktop, and mobile
Steps
Once connected (see setup above), use the Lighthouse Audit tool:
- Ask Claude: "Run a Lighthouse audit on mysite.com and identify render-blocking resources"
- Claude lists every CSS and JS file blocking the first paint with estimated delay
- Ask: "How should I load these resources to eliminate render blocking?"
- Claude suggests async/defer attributes, critical CSS inlining, and preload hints
Example Prompt
Try this with Claude using the Lighthouse Audit tool
Find all render-blocking resources on mysite.com. For each one, tell me how to fix it to speed up first paint.
Tips
- Ask Claude to generate the exact script and link tag attributes needed
- Claude can extract and inline critical CSS for above-the-fold content
- Focus on the resources with the highest estimated blocking time first