SNI Checker

Check SNI requirements and Subject Alternative Names

About SNI Checker

Server Name Indication (SNI) is a TLS extension that allows a client to specify the hostname it is trying to reach during the handshake. This enables servers to host multiple SSL certificates on the same IP address. Our SNI Checker tests whether a server requires SNI to serve the correct certificate, verifies SAN coverage, and helps identify configuration issues with multi-tenant hosting setups.

How to Use

Enter the domain name you want to test.
Click "Check" to perform the SNI analysis.
Review the results showing whether SNI is required, what certificate is served, and the list of covered domains.
Use the findings to troubleshoot multi-domain hosting or certificate issues.

Use Cases

•Verify SNI configuration on shared hosting and CDN setups
•Debug certificate mismatch errors caused by missing SNI
•Test compatibility with legacy clients that do not support SNI
•Audit SAN coverage across all domains hosted on a single IP

Frequently Asked Questions

Server Name Indication (SNI) is an extension to the TLS protocol that lets a client specify the hostname it wants to connect to during the handshake. This allows a server to present the correct SSL certificate when multiple domains are hosted on the same IP address.

Almost all modern browsers support SNI, including Chrome, Firefox, Safari, and Edge. However, some older browsers (notably Internet Explorer on Windows XP and some Android browsers) do not support SNI, which can cause certificate errors on shared hosting environments.

If a server requires SNI but the client does not send it, the server typically serves a default certificate that may not match the requested domain. This results in a certificate name mismatch warning or error in the client.

Tips & Best Practices

•Enable SNI to support multiple SSL certificates on one IP address
•Test SNI functionality from different client configurations
•Monitor SNI usage for virtual hosting and multi-tenant environments
•Configure proper fallback for clients that do not support SNI

Technical Details

Extension: Server Name Indication (SNI) support detection
Virtual Hosting: Multiple certificate support on single IP
Client Support: SNI support detection for different clients
Output: SNI support status with configuration recommendations