1. [JA3 Fingerprint](https://scrapfly.io/web-scraping-tools/ja3-fingerprint)
2. [ TLS Extensions ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extensions "Browse all TLS Extensions")
3. server\_name
 
   [  Browse All TLS Extensions ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extensions) 

  # server\_name

TLS Extension Code: `0`

 

  ### Extension Details

 

Extension Name

`server_name`

 

Extension Code (Decimal)

`0`

 

Extension Code (Hex)

`0x0000`

 

RFC Reference

 [ RFC 6066  ](https://datatracker.ietf.org/doc/html/rfc6066) 

 

 

 

  ### What is server\_name?

 

Server Name Indication (SNI) extension allows the client to indicate which hostname it is attempting to connect to at the start of the TLS handshake. This is crucial for virtual hosting, where multiple HTTPS sites share the same IP address. Without SNI, the server cannot determine which certificate to present. SNI is defined in RFC 6066 and is supported by all modern browsers. However, SNI is transmitted in cleartext, which can reveal browsing history to network observers. TLS 1.3 introduces Encrypted SNI (ESNI) to address this privacy concern.

 

 

  ### Role in JA3 Fingerprinting

 

  How This Extension Affects Fingerprinting 

 The **server\_name** extension is part of the TLS Client Hello packet that JA3 analyzes to create a unique fingerprint of your browser or HTTP client.

 **JA3 Construction:** JA3 concatenates TLS parameters including extensions in a specific format:
 `TLS_VERSION,CIPHERS,EXTENSIONS,CURVES,POINT_FORMATS`

 Different browsers and HTTP clients support different sets of TLS extensions, making this a key differentiator in fingerprinting. The presence, absence, or order of extensions like `server_name` can reveal:

- Browser type and version (Chrome, Firefox, Safari, Edge)
- Operating system (Windows, macOS, Linux, Android, iOS)
- HTTP library (curl, Python requests, Go http.Client, Node.js)
- Bot detection - automated tools often have distinctive extension sets
 
 

 

 

  ### Test Your TLS Configuration

 

 See if your browser or HTTP client includes the `server_name` extension in its TLS handshake:

 [  Test Your JA3 Fingerprint ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint) 

 The JA3 tool will show all TLS extensions your client advertises, including server\_name.

 

  ### Browser & Client Support

 

**Modern Browser Support:**

- **Chrome/Edge:** Full support for server\_name
- **Firefox:** Full support for server\_name
- **Safari:** Full support for server\_name
 
**HTTP Client Libraries:**

- **curl:** Support varies by OpenSSL/LibreSSL version
- **Python requests:** Limited TLS extension control
- **curl\_cffi:** Can mimic browser TLS configurations
- **Scrapfly API:** Automatically matches real browser TLS fingerprints
 
 

 

 

  ### Related TLS Resources

 

##### TLS Extensions

- [server\_name (SNI)](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/server-name)
- [supported\_groups](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/supported-groups)
- [ALPN](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/application-layer-protocol-negotiation)
- [supported\_versions](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/supported-versions)
 
 

##### Testing Tools

- [JA3 Fingerprint Tool](https://scrapfly.io/web-scraping-tools/ja3-fingerprint)
- [Browser Fingerprint Test](https://scrapfly.io/web-scraping-tools/browser-fingerprint)
 
 

 

 

  ### Technical References

 

- **RFC Specification:** [ RFC 6066 - TLS Extensions  ](https://datatracker.ietf.org/doc/html/rfc6066)
- **IANA Registry:** [ TLS ExtensionType Values  ](https://www.iana.org/assignments/tls-extensiontype-values/tls-extensiontype-values.xhtml)
- **JA3 Project:** [ JA3 - TLS Client Fingerprinting  ](https://github.com/salesforce/ja3)