Certificate Compression Checker

Check if TLS certificate compression is supported

About Certificate Compression

TLS certificate compression reduces the size of certificates during the TLS handshake, decreasing latency and improving page load times. The compression is negotiated during the TLS handshake, and both client and server must support it. Our Certificate Compression Checker tests whether a server advertises support for certificate compression, helping you identify opportunities to optimize TLS performance.

How to Use

Enter the domain name you want to test (e.g., example.com).
Optionally change the port number (default is 443 for HTTPS).
Click the Check button to run the test.
Review the results showing whether certificate compression is supported and which compression methods are available.

Use Cases

Performance Optimization: Identify servers that can benefit from certificate compression to reduce TLS handshake size.
Mobile Optimization: Reduce bandwidth usage for mobile clients with compressed certificate chains.
CDN Configuration: Verify that your CDN or reverse proxy supports certificate compression for edge connections.
Security Auditing: Include compression support checks as part of your TLS configuration audit.

Frequently Asked Questions

TLS certificate compression is a mechanism defined in RFC 8879 that reduces the size of certificate chains during the TLS handshake. It uses algorithms like zlib or brotli to compress certificates, resulting in faster handshakes and reduced bandwidth usage.

Large certificate chains can add hundreds of kilobytes to the TLS handshake. Compression reduces this overhead, improving page load times especially on slow connections, mobile networks, and for users accessing sites with complex certificate hierarchies.

Support depends on the TLS library and server software. Modern versions of OpenSSL (3.0+), BoringSSL, and recent web servers like Nginx (with patches) may support it. Use this checker to verify if a specific server has compression enabled.

Tips & Best Practices

•Certificate compression is most beneficial for chains with 2+ intermediates
•Cloudflare enables compression automatically for eligible certificates
•Check OpenSSL version support before implementing on self-hosted servers
•Monitor performance metrics before and after enabling compression

Technical Details

Extension: TLS certificate_compression (RFC 8879)
Algorithms: Brotli and zlib compression analysis
Analysis: Certificate structure, chain length, compression ratio estimation
Servers: Nginx 1.19.4+, Apache with OpenSSL 1.1.1+