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.

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

Rule page: https://frontendchecklist.io/en/rules/performance/preconnect