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Get Started Free →Use when auditing slow page loads, heavy assets, or rendering delays related to Eliminate render-blocking resources. Verify the actual bottleneck in DevTools, Lighthouse, or field data before recommending changes.
| Test case | Without → With | Effect | Δ tokens | Δ turns |
|---|---|---|---|---|
| case-15 | ✗→✓ | ▲ Improved | -9% | 0% |
| case-01 | ✓→✓ | ＝ Same ✓ | 17% | 0% |
| case-02 | ✓→✓ | ＝ Same ✓ | 24% | 0% |
| case-03 | ✓→✓ | ＝ Same ✓ | 1% | 0% |
| case-04 | ✓→✓ | ＝ Same ✓ | -34% | 0% |
Render-blocking resources prevent the browser from painting anything on the screen, leading to a "white screen" effect and poor user experience.
defer, async, or media queries@import in CSS as it creates serial request chainsReview the page's resources and identify any CSS or JavaScript files that are blocking the initial render of the page.
Update the loading strategy for render-blocking resources by using defer, async, or inlining critical styles.
Explain how render-blocking resources impact the First Contentful Paint (FCP) and how to resolve them.
Review the routes, assets, and loading behavior that affect Eliminate render-blocking resources. Flag exact files, requests, or rendering steps that add unnecessary network, CPU, or layout cost, and describe the measurement method used to confirm the issue.
For full implementation details, code examples, and framework-specific guidance, see references/rule.md.
Rule page: https://frontendchecklist.io/en/rules/performance/render-blocking
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