1. [JA3 Fingerprint](https://scrapfly.io/web-scraping-tools/ja3-fingerprint) 2. TLS Extensions # TLS Extensions Database Complete reference of 26 IANA-registered TLS extensions ### About TLS Extensions TLS extensions are optional features that clients and servers can negotiate during the TLS handshake. They extend the core TLS protocol to support additional capabilities like Server Name Indication (SNI), Application-Layer Protocol Negotiation (ALPN), and more. In **JA3 fingerprinting**, the set of TLS extensions advertised by a client is a key component of the fingerprint. Different browsers and HTTP libraries support different extensions, making this a reliable way to identify and differentiate clients. **JA3 Format:** `TLS_VERSION,CIPHERS,EXTENSIONS,CURVES,POINT_FORMATS` ### Search TLS Extensions Try searching for: "server\_name", "SNI", "0x0000", "23", "ALPN", or "grease" ### All TLS Extensions (26) | Extension Name | Code (Dec) | Code (Hex) | Description | RFC | |---|---|---|---|---| | [ Server Name Indication (SNI) ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/server-name) `server_name` | `0` | `0x0000` | Server Name Indication (SNI) extension allows the client to indicate which hostname it is attempting... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc6066) | | [ Maximum Fragment Length ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/max-fragment-length) `max_fragment_length` | `1` | `0x0001` | The Maximum Fragment Length extension allows clients with limited buffer sizes to negotiate a smalle... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc6066) | | [ OCSP Stapling (Certificate Status Request) ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/status-request) `status_request` | `5` | `0x0005` | The Certificate Status Request extension, also known as OCSP Stapling, allows the client to request ... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc6066) | | [ Supported Groups (Elliptic Curves) ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/supported-groups) `supported_groups` | `10` | `0x000A` | The Supported Groups extension (formerly called Elliptic Curves) indicates which elliptic curve grou... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc8446#section-4.2.7) | | [ EC Point Formats ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/ec-point-formats) `ec_point_formats` | `11` | `0x000B` | The EC Point Formats extension specifies which elliptic curve point formats the client can parse. Th... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc8422) | | [ Signature Algorithms ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/signature-algorithms) `signature_algorithms` | `13` | `0x000D` | The Signature Algorithms extension indicates which signature algorithms the client supports for veri... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc8446#section-4.2.3) | | [ ALPN (Application-Layer Protocol Negotiation) ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/application-layer-protocol-negotiation) `application_layer_protocol_negotiation` | `16` | `0x0010` | ALPN (Application-Layer Protocol Negotiation) allows the client and server to negotiate which applic... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc7301) | | [ Signed Certificate Timestamp (SCT) ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/signed-certificate-timestamp) `signed_certificate_timestamp` | `18` | `0x0012` | The Signed Certificate Timestamp (SCT) extension enables Certificate Transparency by allowing client... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc6962) | | [ Extended Master Secret (EMS) ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/extended-master-secret) `extended_master_secret` | `23` | `0x0017` | The Extended Master Secret extension addresses the "Triple Handshake Attack" vulnerability in TLS 1.... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc7627) | | [ Certificate Compression ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/compress-certificate) `compress_certificate` | `27` | `0x001B` | The Compress Certificate extension allows TLS certificate chains to be compressed using algorithms l... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc8879) | | [ Record Size Limit ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/record-size-limit) `record_size_limit` | `28` | `0x001C` | The Record Size Limit extension allows clients and servers to negotiate the maximum size of TLS reco... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc8449) | | [ Session Ticket ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/session-ticket) `session_ticket` | `35` | `0x0023` | The Session Ticket extension enables stateless TLS session resumption. Instead of the server maintai... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc5077) | | [ Pre-Shared Key (PSK) ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/pre-shared-key) `pre_shared_key` | `41` | `0x0029` | The Pre-Shared Key (PSK) extension in TLS 1.3 enables fast session resumption and 0-RTT (Zero Round-... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc8446#section-4.2.11) | | [ Early Data (0-RTT) ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/early-data) `early_data` | `42` | `0x002A` | The Early Data extension (also known as 0-RTT) allows clients to send application data in the first ... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc8446#section-4.2.10) | | [ Supported Versions ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/supported-versions) `supported_versions` | `43` | `0x002B` | The Supported Versions extension allows clients to indicate which TLS versions they support. In TLS ... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc8446#section-4.2.1) | | [ Cookie ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/cookie) `cookie` | `44` | `0x002C` | The Cookie extension in TLS 1.3 is used for stateless handshake retries when the server is under loa... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc8446#section-4.2.2) | | [ Certificate Authorities ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/certificate-authorities) `certificate_authorities` | `47` | `0x002F` | The Certificate Authorities extension allows clients to indicate which certificate authorities (CAs)... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc8446#section-4.2.4) | | [ Key Share ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/key-share) `key_share` | `51` | `0x0033` | The Key Share extension in TLS 1.3 contains the client's cryptographic key exchange parameters for (... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc8446#section-4.2.8) | | [ PSK Key Exchange Modes ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/psk-key-exchange-modes) `psk_key_exchange_modes` | `45` | `0x002D` | The PSK Key Exchange Modes extension specifies which modes the client supports when using PSK (Pre-S... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc8446#section-4.2.9) | | [ Renegotiation Info ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/renegotiation-info) `renegotiation_info` | `65281` | `0xFF01` | The Renegotiation Info extension prevents the TLS renegotiation attack discovered in 2009. Without t... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc5746) | | [ Padding ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/padding) `padding` | `21` | `0x0015` | The Padding extension allows clients to pad the Client Hello message to a desired size. This is used... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc7685) | | [ Application Settings (ALPS) ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/application-settings) `application_settings` | `17513` | `0x4469` | Application Settings (ALPS) is a Chrome-introduced TLS extension that lets the server hint applicati... | [ draft-vvv-tls-alps ](https://datatracker.ietf.org/doc/html/draft-vvv-tls-alps) | | [ Application Settings (ALPS, new codepoint) ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/application-settings-new-codepoint) `application_settings_new_codepoint` | `17613` | `0x44CD` | Application Settings (ALPS), re-codepointed at 17613. Recent Chrome builds emit the same Application... | [ draft-vvv-tls-alps ](https://datatracker.ietf.org/doc/html/draft-vvv-tls-alps) | | [ Encrypted Client Hello (ECH) ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/encrypted-client-hello) `encrypted_client_hello` | `65037` | `0xFE0D` | Encrypted Client Hello (ECH) hides the contents of the TLS Client Hello — including SNI and ALPN — f... | [ draft-ietf-tls-esni ](https://datatracker.ietf.org/doc/html/draft-ietf-tls-esni) | | [ Trust Anchors ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/trust-anchors) `trust_anchors` | `51764` | `0xCA34` | Trust Anchors (codepoint 51764 / 0xCA34) lets the client advertise which certificate-authority trust... | [ draft-ietf-tls-trust-anchor-ids ](https://datatracker.ietf.org/doc/html/draft-ietf-tls-trust-anchor-ids) | | [ QUIC Transport Parameters ](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/extension/quic-transport-parameters) `quic_transport_parameters` | `57` | `0x0039` | QUIC Transport Parameters is a TLS extension carried inside the TLS 1.3 handshake when TLS is being ... | [ RFC ](https://datatracker.ietf.org/doc/html/rfc9001) | No extensions found matching your search. Try searching for extension names (e.g., "server\_name"), codes (e.g., "23"), or keywords. ### Related Resources ##### TLS Fingerprinting - [JA3 Fingerprint Tool](https://scrapfly.io/web-scraping-tools/ja3-fingerprint) - [Browse All Cipher Suites](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/cipher-suites) - [Browse All Supported Groups](https://scrapfly.io/web-scraping-tools/ja3-fingerprint/supported-groups) ##### External References - [IANA TLS ExtensionType Values ](https://www.iana.org/assignments/tls-extensiontype-values/tls-extensiontype-values.xhtml) - [JA3 - TLS Client Fingerprinting ](https://github.com/salesforce/ja3)