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. application\_layer\_protocol\_negotiation
 
   [  Browse All TLS Extensions ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extensions) 

  # application\_layer\_protocol\_negotiation

TLS Extension Code: `16`

 

  ### Extension Details

 

Extension Name

`application_layer_protocol_negotiation`

 

Extension Code (Decimal)

`16`

 

Extension Code (Hex)

`0x0010`

 

RFC Reference

 [ RFC 7301  ](https://datatracker.ietf.org/doc/html/rfc7301) 

 

 

 

  ### What is application\_layer\_protocol\_negotiation?

 

ALPN (Application-Layer Protocol Negotiation) allows the client and server to negotiate which application protocol (HTTP/1.1, HTTP/2, HTTP/3) will be used over the TLS connection. This eliminates an extra round trip compared to NPN (Next Protocol Negotiation). Common ALPN values include "h2" (HTTP/2), "http/1.1", and "h3" (HTTP/3). Browsers typically advertise multiple protocols in order of preference: h2, http/1.1. ALPN is defined in RFC 7301 and is essential for modern web performance. ALPN values are also used in TLS fingerprinting to identify clients.

 

 

  ### Role in JA3 Fingerprinting

 

  How This Extension Affects Fingerprinting 

 The **application\_layer\_protocol\_negotiation** 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 `application_layer_protocol_negotiation` 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 `application_layer_protocol_negotiation` 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 application\_layer\_protocol\_negotiation.

 

  ### Browser & Client Support

 

**Modern Browser Support:**

- **Chrome/Edge:** Full support for application\_layer\_protocol\_negotiation
- **Firefox:** Full support for application\_layer\_protocol\_negotiation
- **Safari:** Full support for application\_layer\_protocol\_negotiation
 
**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 7301 - TLS Extensions  ](https://datatracker.ietf.org/doc/html/rfc7301)
- **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)