0-RTT Checker

Check if TLS 1.3 early data (0-RTT) is supported

About 0-RTT Checker

The 0-RTT (Zero Round-Trip Time) Checker tests whether a server supports TLS 1.3 early data, which allows clients to send data immediately after the ClientHello without waiting for the handshake to complete. This feature reduces latency for returning visitors but requires careful anti-replay protection.

Use Cases

•Verify TLS 1.3 early data support on your web server
•Measure latency improvements from 0-RTT resumption
•Check anti-replay protection configuration
•Optimize TLS handshake performance for returning users

How to Use

•Enter the domain name you want to test for 0-RTT support
•Click "Check" to perform the early data test
•Review the results showing 0-RTT support status and anti-replay settings

Frequently Asked Questions

0-RTT (Zero Round-Trip Time) is a TLS 1.3 feature that allows clients to send data to the server immediately after the ClientHello, without waiting for the handshake to complete. This reduces connection latency for returning visitors who have previously established a session.

0-RTT can be vulnerable to replay attacks if not properly protected. The TLS 1.3 specification requires servers to implement anti-replay mechanisms. Our checker verifies whether the server has proper anti-replay protection alongside 0-RTT support.

0-RTT can reduce connection latency by one full round trip compared to a full TLS 1.3 handshake. For geographically distributed users, this can mean 50-200ms reduction in time-to-first-byte, significantly improving perceived performance for returning visitors.

Tips & Best Practices

•Enable 0-RTT early data for faster TLS handshakes on repeat connections
•Understand the security implications of replay attacks with early data
•Configure replay protection for applications accepting early data
•Monitor early data usage for performance optimization

Technical Details

TLS Extension: Early Data (0-RTT) support detection
Security: Replay attack risk assessment and protection
Performance: Handshake time reduction measurement
Output: Early data status with security and performance analysis

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