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name: third-party-scripts description: "Use when auditing slow page loads, heavy assets, or rendering delays related to Optimize third-party script loading. Verify the actual bottleneck in DevTools, Lighthouse, or field data before recommending changes." metadata: category: performance priority: high difficulty: intermediate estimatedTime: "20" source: frontendchecklist.io url: https://frontendchecklist.io/rules/performance/third-party-scripts

Optimize third-party script loading

Third-party scripts are the #1 cause of slow websites—unoptimized loading can add 2-5 seconds to your page load time.

Quick Reference

• Use async for independent scripts (analytics, ads)
• Use defer for DOM-dependent scripts (chat widgets, social)
• Lazy-load non-critical scripts after page load
• Consider self-hosting critical third-party scripts

Check

Analyze third-party scripts on this page to ensure they use async/defer and don't block rendering.

Fix

Add async or defer attributes to third-party scripts and consider lazy loading non-critical scripts.

Explain

Explain the performance impact of third-party scripts and strategies to minimize their blocking effect.

Code Review

Review the routes, assets, and loading behavior that affect Optimize third-party script loading. 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.

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For full implementation details, code examples, and framework-specific guidance, see references/rule.md.

Rule page: https://frontendchecklist.io/rules/performance/third-party-scripts