Use preconnect for critical third-party origins

Preconnecting to essential origins can shave hundreds of milliseconds off the critical path by handling connection overhead ahead of time.

Quick Reference

• Establish early connections to important third-party domains (e.g., fonts, APIs)
• Reduce latency by performing DNS lookup, TCP handshake, and TLS negotiation early
• Avoid overusing preconnect; limit to 2-4 most critical origins

Check

Review the page's head for preconnect hints and identify any missing or unnecessary connections to third-party domains.

Fix

Add <link rel="preconnect"> for critical third-party origins and remove it for non-essential or underutilized domains.

Explain

Explain how preconnect helps reduce the time spent on connection overhead for third-party resources.

Code Review

Review the routes, assets, and loading behavior that affect Use preconnect for critical third-party origins. 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/en/rules/performance/preconnect