| A-IM | permanent | | [RFC 3229: Delta encoding in HTTP] | |
| Accept | permanent | | [RFC 9110, Section 12.5.1: HTTP Semantics] | |
| Accept-Additions | permanent | | [RFC 2324: Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)] | |
| Accept-CH | permanent | List | [RFC 8942, Section 3.1: HTTP Client Hints] | |
| Accept-Charset | deprecated | | [RFC 9110, Section 12.5.2: HTTP Semantics] | |
| Accept-Datetime | permanent | | [RFC 7089: HTTP Framework for Time-Based Access to Resource States -- Memento] | |
| Accept-Encoding | permanent | | [RFC 9110, Section 12.5.3: HTTP Semantics] | |
| Accept-Features | permanent | | [RFC 2295: Transparent Content Negotiation in HTTP] | |
| Accept-Language | permanent | | [RFC 9110, Section 12.5.4: HTTP Semantics] | |
| Accept-Patch | permanent | | [RFC 5789: PATCH Method for HTTP] | |
| Accept-Post | permanent | | [Linked Data Platform 1.0] | |
| Accept-Query | permanent | List | [RFC-ietf-httpbis-safe-method-w-body-14, Section 3: The HTTP QUERY Method] | |
| Accept-Ranges | permanent | | [RFC 9110, Section 14.3: HTTP Semantics] | |
| Accept-Signature | permanent | | [RFC 9421, Section 5.1: HTTP Message Signatures] | |
| Access-Control | obsoleted | | [Access Control for Cross-site Requests] | |
| Access-Control-Allow-Credentials | permanent | | [Fetch] | |
| Access-Control-Allow-Headers | permanent | | [Fetch] | |
| Access-Control-Allow-Methods | permanent | | [Fetch] | |
| Access-Control-Allow-Origin | permanent | | [Fetch] | |
| Access-Control-Expose-Headers | permanent | | [Fetch] | |
| Access-Control-Max-Age | permanent | | [Fetch] | |
| Access-Control-Request-Headers | permanent | | [Fetch] | |
| Access-Control-Request-Method | permanent | | [Fetch] | |
| Activate-Storage-Access | provisional | Item | [https://privacycg.github.io/storage-access-headers] | |
| Age | permanent | | [RFC 9111, Section 5.1: HTTP Caching] | |
| Allow | permanent | | [RFC 9110, Section 10.2.1: HTTP Semantics] | |
| ALPN | permanent | | [RFC 7639, Section 2: The ALPN HTTP Header Field] | |
| Alt-Svc | permanent | | [RFC 7838: HTTP Alternative Services] | |
| Alt-Used | permanent | | [RFC 7838: HTTP Alternative Services] | |
| Alternates | permanent | | [RFC 2295: Transparent Content Negotiation in HTTP] | |
| AMP-Cache-Transform | provisional | | [AMP-Cache-Transform HTTP request header] | |
| Apply-To-Redirect-Ref | permanent | | [RFC 4437: Web Distributed Authoring and Versioning (WebDAV) Redirect Reference Resources] | |
| Authentication-Control | permanent | | [RFC 8053, Section 4: HTTP Authentication Extensions for Interactive Clients] | |
| Authentication-Info | permanent | | [RFC 9110, Section 11.6.3: HTTP Semantics] | |
| Authorization | permanent | | [RFC 9110, Section 11.6.2: HTTP Semantics] | |
| Available-Dictionary | permanent | | [RFC 9842, Section 2.2: Compression Dictionary Transport] | |
| C-Ext | obsoleted | | [RFC 2774: An HTTP Extension Framework] | [Status change of HTTP experiments to Historic] |
| C-Man | obsoleted | | [RFC 2774: An HTTP Extension Framework] | [Status change of HTTP experiments to Historic] |
| C-Opt | obsoleted | | [RFC 2774: An HTTP Extension Framework] | [Status change of HTTP experiments to Historic] |
| C-PEP | obsoleted | | [PEP - an Extension Mechanism for HTTP] | [Status change of HTTP experiments to Historic] |
| C-PEP-Info | deprecated | | [PEP - an Extension Mechanism for HTTP] | [Status change of HTTP experiments to Historic] |
| Cache-Control | permanent | | [RFC 9111, Section 5.2: HTTP Caching] | |
| Cache-Group-Invalidation | permanent | | [RFC9875: HTTP Cache Groups] | |
| Cache-Groups | permanent | | [RFC9875: HTTP Cache Groups] | |
| Cache-Status | permanent | List | [RFC 9211: The Cache-Status HTTP Response Header Field] | |
| Cal-Managed-ID | permanent | | [RFC 8607, Section 5.1: Calendaring Extensions to WebDAV (CalDAV): Managed Attachments] | |
| CalDAV-Timezones | permanent | | [RFC 7809, Section 7.1: Calendaring Extensions to WebDAV (CalDAV): Time Zones by Reference] | |
| Capsule-Protocol | permanent | | [RFC 9297: HTTP Datagrams and the Capsule Protocol] | |
| CDN-Cache-Control | permanent | Dictionary | [RFC 9213: Targeted HTTP Cache Control] | Cache directives targeted at content delivery networks |
| CDN-Loop | permanent | | [RFC 8586: Loop Detection in Content Delivery Networks (CDNs)] | |
| Cert-Not-After | permanent | | [RFC 8739, Section 3.3: Support for Short-Term, Automatically Renewed (STAR) Certificates in the Automated Certificate Management Environment (ACME)] | |
| Cert-Not-Before | permanent | | [RFC 8739, Section 3.3: Support for Short-Term, Automatically Renewed (STAR) Certificates in the Automated Certificate Management Environment (ACME)] | |
| Clear-Site-Data | permanent | | [Clear Site Data] | |
| Client-Cert | permanent | Item | [RFC 9440, Section 2: Client-Cert HTTP Header Field] | |
| Client-Cert-Chain | permanent | List | [RFC 9440, Section 2: Client-Cert HTTP Header Field] | |
| Close | permanent | | [RFC 9112, Section 9.6: HTTP/1.1] | (reserved) |
| CMCD-Object | provisional | | [CTA][CTA-5004 Common Media Client Data] | |
| CMCD-Request | provisional | | [CTA][CTA-5004 Common Media Client Data] | |
| CMCD-Session | provisional | | [CTA][CTA-5004 Common Media Client Data] | |
| CMCD-Status | provisional | | [CTA][CTA-5004 Common Media Client Data] | |
| CMSD-Dynamic | provisional | | [CTA][CTA-5006 Common Media Server Data (CMSD)] | |
| CMSD-Static | provisional | | [CTA][CTA-5006 Common Media Server Data (CMSD)] | |
| Concealed-Auth-Export | permanent | Item | [RFC 9729: The Concealed HTTP Authentication Scheme] | |
| Configuration-Context | provisional | | [OSLC Configuration Management Version 1.0. Part 3: Configuration Specification] | |
| Connection | permanent | | [RFC 9110, Section 7.6.1: HTTP Semantics] | |
| Content-Base | obsoleted | | [RFC 2068: Hypertext Transfer Protocol -- HTTP/1.1] | Obsoleted by [RFC 2616: Hypertext Transfer Protocol -- HTTP/1.1] |
| Content-Digest | permanent | | [RFC 9530, Section 2: Digest Fields] | |
| Content-Disposition | permanent | | [RFC 6266: Use of the Content-Disposition Header Field in the Hypertext Transfer Protocol (HTTP)] | |
| Content-Encoding | permanent | | [RFC 9110, Section 8.4: HTTP Semantics] | |
| Content-ID | deprecated | | [The HTTP Distribution and Replication Protocol] | |
| Content-Language | permanent | | [RFC 9110, Section 8.5: HTTP Semantics] | |
| Content-Length | permanent | | [RFC 9110, Section 8.6: HTTP Semantics] | |
| Content-Location | permanent | | [RFC 9110, Section 8.7: HTTP Semantics] | |
| Content-MD5 | obsoleted | | [RFC 2616, Section 14.15: Hypertext Transfer Protocol -- HTTP/1.1] | Obsoleted by [RFC 7231, Appendix B: Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content] |
| Content-Range | permanent | | [RFC 9110, Section 14.4: HTTP Semantics] | |
| Content-Script-Type | obsoleted | | [HTML 4.01 Specification] | |
| Content-Security-Policy | permanent | | [Content Security Policy Level 3] | |
| Content-Security-Policy-Report-Only | permanent | | [Content Security Policy Level 3] | |
| Content-Style-Type | obsoleted | | [HTML 4.01 Specification] | |
| Content-Type | permanent | | [RFC 9110, Section 8.3: HTTP Semantics] | |
| Content-Version | obsoleted | | [RFC 2068: Hypertext Transfer Protocol -- HTTP/1.1] | |
| Cookie | permanent | | [RFC-ietf-httpbis-rfc6265bis-22, Section 5.8.1: Cookies: HTTP State Management Mechanism] | |
| Cookie2 | obsoleted | | [RFC 2965: HTTP State Management Mechanism] | Obsoleted by [RFC 6265: HTTP State Management Mechanism] |
| Cross-Origin-Embedder-Policy | permanent | Item | [HTML] | |
| Cross-Origin-Embedder-Policy-Report-Only | permanent | Item | [HTML] | |
| Cross-Origin-Opener-Policy | permanent | Item | [HTML] | |
| Cross-Origin-Opener-Policy-Report-Only | permanent | Item | [HTML] | |
| Cross-Origin-Resource-Policy | permanent | | [Fetch] | |
| CTA-Common-Access-Token | provisional | | [CTA][Chris_Lemmons] | |
| DASL | permanent | | [RFC 5323: Web Distributed Authoring and Versioning (WebDAV) SEARCH] | |
| Date | permanent | | [RFC 9110, Section 6.6.1: HTTP Semantics] | |
| DAV | permanent | | [RFC 4918: HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)] | |
| Default-Style | obsoleted | | [HTML 4.01 Specification] | |
| Delta-Base | permanent | | [RFC 3229: Delta encoding in HTTP] | |
| Deprecation | permanent | Item | [RFC 9745, Section 2: The Deprecation HTTP Response Header Field] | |
| Depth | permanent | | [RFC 4918: HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)] | |
| Derived-From | obsoleted | | [RFC 2068: Hypertext Transfer Protocol -- HTTP/1.1] | |
| Destination | permanent | | [RFC 4918: HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)] | |
| Detached-JWS | permanent | | [RFC 9635: Grant Negotiation and Authorization Protocol (GNAP)] | |
| Differential-ID | deprecated | | [The HTTP Distribution and Replication Protocol] | |
| Dictionary-ID | permanent | | [RFC 9842, Section 2.3: Compression Dictionary Transport] | |
| Digest | obsoleted | | [RFC 3230: Instance Digests in HTTP] | Obsoleted by [RFC 9530, Section 1.3: Digest Fields] |
| DPoP | permanent | | [RFC 9449: OAuth 2.0 Demonstrating Proof of Possession (DPoP)] | |
| DPoP-Nonce | permanent | | [RFC 9449: OAuth 2.0 Demonstrating Proof of Possession (DPoP)] | |
| Early-Data | permanent | | [RFC 8470: Using Early Data in HTTP] | |
| EDIINT-Features | provisional | | [RFC 6017: Electronic Data Interchange - Internet Integration (EDIINT) Features Header Field] | |
| ETag | permanent | | [RFC 9110, Section 8.8.3: HTTP Semantics] | |
| Expect | permanent | | [RFC 9110, Section 10.1.1: HTTP Semantics] | |
| Expect-CT | deprecated | | [RFC 9163: Expect-CT Extension for HTTP] | Obsoleted by [IESG] [HTTPBIS] |
| Expires | permanent | | [RFC 9111, Section 5.3: HTTP Caching] | |
| Ext | obsoleted | | [RFC 2774: An HTTP Extension Framework] | [Status change of HTTP experiments to Historic] |
| Forwarded | permanent | | [RFC 7239: Forwarded HTTP Extension] | |
| From | permanent | | [RFC 9110, Section 10.1.2: HTTP Semantics] | |
| GetProfile | obsoleted | | [Implementation of OPS Over HTTP] | |
| Hobareg | permanent | | [RFC 7486, Section 6.1.1: HTTP Origin-Bound Authentication (HOBA)] | |
| Host | permanent | | [RFC 9110, Section 7.2: HTTP Semantics] | |
| HTTP2-Settings | obsoleted | | [RFC 7540, Section 3.2.1: Hypertext Transfer Protocol Version 2 (HTTP/2)] | Obsolete; see Section 11.1 of [RFC9113] |
| If | permanent | | [RFC 4918: HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)] | |
| If-Match | permanent | | [RFC 9110, Section 13.1.1: HTTP Semantics] | |
| If-Modified-Since | permanent | | [RFC 9110, Section 13.1.3: HTTP Semantics] | |
| If-None-Match | permanent | | [RFC 9110, Section 13.1.2: HTTP Semantics] | |
| If-Range | permanent | | [RFC 9110, Section 13.1.5: HTTP Semantics] | |
| If-Schedule-Tag-Match | permanent | | [ RFC 6338: Scheduling Extensions to CalDAV] | |
| If-Unmodified-Since | permanent | | [RFC 9110, Section 13.1.4: HTTP Semantics] | |
| IM | permanent | | [RFC 3229: Delta encoding in HTTP] | |
| Include-Referred-Token-Binding-ID | permanent | | [RFC 8473: Token Binding over HTTP] | |
| Isolation | provisional | | [OData Version 4.01 Part 1: Protocol][OASIS][Chet_Ensign] | |
| Keep-Alive | permanent | | [RFC 2068: Hypertext Transfer Protocol -- HTTP/1.1] | |
| Label | permanent | | [RFC 3253: Versioning Extensions to WebDAV: (Web Distributed Authoring and Versioning)] | |
| Last-Event-ID | permanent | | [HTML] | |
| Last-Modified | permanent | | [RFC 9110, Section 8.8.2: HTTP Semantics] | |
| Link | permanent | | [RFC 8288: Web Linking] | |
| Link-Template | permanent | | [RFC 9652: The Link-Template HTTP Header Field] | |
| Location | permanent | | [RFC 9110, Section 10.2.2: HTTP Semantics] | |
| Lock-Token | permanent | | [RFC 4918: HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)] | |
| Man | obsoleted | | [RFC 2774: An HTTP Extension Framework] | [Status change of HTTP experiments to Historic] |
| Max-Forwards | permanent | | [RFC 9110, Section 7.6.2: HTTP Semantics] | |
| Memento-Datetime | permanent | | [RFC 7089: HTTP Framework for Time-Based Access to Resource States -- Memento] | |
| Meter | permanent | | [RFC 2227: Simple Hit-Metering and Usage-Limiting for HTTP] | |
| Method-Check | obsoleted | | [Access Control for Cross-site Requests] | |
| Method-Check-Expires | obsoleted | | [Access Control for Cross-site Requests] | |
| MIME-Version | permanent | | [RFC 9112, Appendix B.1: HTTP/1.1] | |
| Negotiate | permanent | | [RFC 2295: Transparent Content Negotiation in HTTP] | |
| NEL | permanent | | [Network Error Logging] | |
| OData-EntityId | permanent | | [OData Version 4.01 Part 1: Protocol][OASIS][Chet_Ensign] | |
| OData-Isolation | permanent | | [OData Version 4.01 Part 1: Protocol][OASIS][Chet_Ensign] | |
| OData-MaxVersion | permanent | | [OData Version 4.01 Part 1: Protocol][OASIS][Chet_Ensign] | |
| OData-Version | permanent | | [OData Version 4.01 Part 1: Protocol][OASIS][Chet_Ensign] | |
| Opt | obsoleted | | [RFC 2774: An HTTP Extension Framework] | [Status change of HTTP experiments to Historic] |
| Optional-WWW-Authenticate | permanent | | [RFC 8053, Section 3: HTTP Authentication Extensions for Interactive Clients] | |
| Ordering-Type | permanent | | [RFC 3648: Web Distributed Authoring and Versioning (WebDAV) Ordered Collections Protocol] | |
| Origin | permanent | | [RFC 6454: The Web Origin Concept] | |
| Origin-Agent-Cluster | permanent | Item | [HTML] | |
| OSCORE | permanent | | [RFC 8613, Section 11.1: Object Security for Constrained RESTful Environments (OSCORE)] | |
| OSLC-Core-Version | permanent | | [OASIS Project Specification 01][OASIS][Chet_Ensign] | |
| Overwrite | permanent | | [RFC 4918: HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)] | |
| P3P | obsoleted | | [The Platform for Privacy Preferences 1.0 (P3P1.0) Specification] | |
| PEP | obsoleted | | [PEP - an Extension Mechanism for HTTP] | |
| PEP-Info | obsoleted | | [PEP - an Extension Mechanism for HTTP] | |
| Permissions-Policy | provisional | | [Permissions Policy] | |
| PICS-Label | obsoleted | | [PICS Label Distribution Label Syntax and Communication Protocols] | |
| Ping-From | permanent | | [HTML] | |
| Ping-To | permanent | | [HTML] | |
| Position | permanent | | [RFC 3648: Web Distributed Authoring and Versioning (WebDAV) Ordered Collections Protocol] | |
| Pragma | deprecated | | [RFC 9111, Section 5.4: HTTP Caching] | |
| Prefer | permanent | | [RFC 7240: Prefer Header for HTTP] | |
| Preference-Applied | permanent | | [RFC 7240: Prefer Header for HTTP] | |
| Priority | permanent | Dictionary | [RFC 9218: Extensible Prioritization Scheme for HTTP] | |
| ProfileObject | obsoleted | | [Implementation of OPS Over HTTP] | |
| Protocol | obsoleted | | [PICS Label Distribution Label Syntax and Communication Protocols] | |
| Protocol-Info | deprecated | | [White Paper: Joint Electronic Payment Initiative] | |
| Protocol-Query | deprecated | | [White Paper: Joint Electronic Payment Initiative] | |
| Protocol-Request | obsoleted | | [PICS Label Distribution Label Syntax and Communication Protocols] | |
| Proxy-Authenticate | permanent | | [RFC 9110, Section 11.7.1: HTTP Semantics] | |
| Proxy-Authentication-Info | permanent | | [RFC 9110, Section 11.7.3: HTTP Semantics] | |
| Proxy-Authorization | permanent | | [RFC 9110, Section 11.7.2: HTTP Semantics] | |
| Proxy-Features | obsoleted | | [Notification for Proxy Caches] | |
| Proxy-Instruction | obsoleted | | [Notification for Proxy Caches] | |
| Proxy-Status | permanent | List | [RFC 9209: The Proxy-Status HTTP Response Header Field] | |
| Public | obsoleted | | [RFC 2068: Hypertext Transfer Protocol -- HTTP/1.1] | |
| Public-Key-Pins | permanent | | [RFC 7469: Public Key Pinning Extension for HTTP] | |
| Public-Key-Pins-Report-Only | permanent | | [RFC 7469: Public Key Pinning Extension for HTTP] | |
| Range | permanent | | [RFC 9110, Section 14.2: HTTP Semantics] | |
| Redirect-Ref | permanent | | [RFC 4437: Web Distributed Authoring and Versioning (WebDAV) Redirect Reference Resources] | |
| Referer | permanent | | [RFC 9110, Section 10.1.3: HTTP Semantics] | |
| Referer-Root | obsoleted | | [Access Control for Cross-site Requests] | |
| Referrer-Policy | permanent | | [Referrer Policy] | The header name does not share the HTTP Referer header's misspelling. |
| Refresh | permanent | | [HTML] | |
| Repeatability-Client-ID | provisional | | [Repeatable Requests Version 1.0][OASIS][Chet_Ensign] | |
| Repeatability-First-Sent | provisional | | [Repeatable Requests Version 1.0][OASIS][Chet_Ensign] | |
| Repeatability-Request-ID | provisional | | [Repeatable Requests Version 1.0][OASIS][Chet_Ensign] | |
| Repeatability-Result | provisional | | [Repeatable Requests Version 1.0][OASIS][Chet_Ensign] | |
| Replay-Nonce | permanent | | [RFC 8555, Section 6.5.1: Automatic Certificate Management Environment (ACME)] | |
| Reporting-Endpoints | provisional | | [Reporting API] | |
| Repr-Digest | permanent | | [RFC 9530, Section 3: Digest Fields] | |
| Retry-After | permanent | | [RFC 9110, Section 10.2.3: HTTP Semantics] | |
| Safe | obsoleted | | [RFC 2310: The Safe Response Header Field] | [Status change of HTTP experiments to Historic] |
| Schedule-Reply | permanent | | [RFC 6638: Scheduling Extensions to CalDAV] | |
| Schedule-Tag | permanent | | [RFC 6338: Scheduling Extensions to CalDAV] | |
| Sec-Fetch-Dest | Permanent | Item | [https://www.w3.org/TR/fetch-metadata/#sec-fetch-dest-header] | |
| Sec-Fetch-Mode | Permanent | Item | [https://www.w3.org/TR/fetch-metadata/#sec-fetch-mode-header] | |
| Sec-Fetch-Site | Permanent | Item | [https://www.w3.org/TR/fetch-metadata/#sec-fetch-site-header] | |
| Sec-Fetch-Storage-Access | provisional | Token | [https://privacycg.github.io/storage-access-headers] | |
| Sec-Fetch-User | Permanent | Item | [https://www.w3.org/TR/fetch-metadata/#sec-fetch-user-header] | |
| Sec-GPC | provisional | | [Global Privacy Control (GPC)] | |
| Sec-Purpose | permanent | | [Fetch] | Intended to replace the (not registered) Purpose and x-moz headers. |
| Sec-Token-Binding | permanent | | [RFC 8473: Token Binding over HTTP] | |
| Sec-WebSocket-Accept | permanent | | [RFC 6455: The WebSocket Protocol] | |
| Sec-WebSocket-Extensions | permanent | | [RFC 6455: The WebSocket Protocol] | |
| Sec-WebSocket-Key | permanent | | [RFC 6455: The WebSocket Protocol] | |
| Sec-WebSocket-Protocol | permanent | | [RFC 6455: The WebSocket Protocol] | |
| Sec-WebSocket-Version | permanent | | [RFC 6455: The WebSocket Protocol] | |
| Security-Scheme | obsoleted | | [RFC 2660: The Secure HyperText Transfer Protocol] | [Status change of HTTP experiments to Historic] |
| Server | permanent | | [RFC 9110, Section 10.2.4: HTTP Semantics] | |
| Server-Timing | permanent | | [Server Timing] | |
| Set-Cookie | permanent | | [RFC-ietf-httpbis-rfc6265bis-22, Section 5.8.1: Cookies: HTTP State Management Mechanism] | |
| Set-Cookie2 | obsoleted | | [RFC 2965: HTTP State Management Mechanism] | Obsoleted by [RFC 6265: HTTP State Management Mechanism] |
| Set-Txn | permanent | | [RFC-ietf-scim-events-15, Section 3: SCIM Profile for Security Event Tokens] | |
| SetProfile | obsoleted | | [Implementation of OPS Over HTTP] | |
| Signature | permanent | | [RFC 9421, Section 4.2: HTTP Message Signatures] | |
| Signature-Input | permanent | | [RFC 9421, Section 4.1: HTTP Message Signatures] | |
| SLUG | permanent | | [RFC 5023: The Atom Publishing Protocol] | |
| SoapAction | permanent | | [Simple Object Access Protocol (SOAP) 1.1] | |
| Status-URI | permanent | | [RFC 2518: HTTP Extensions for Distributed Authoring -- WEBDAV] | |
| Strict-Transport-Security | permanent | | [RFC 6797: HTTP Strict Transport Security (HSTS)] | |
| Sunset | permanent | | [RFC 8594: The Sunset HTTP Header Field] | |
| Surrogate-Capability | provisional | | [Edge Architecture Specification] | |
| Surrogate-Control | provisional | | [Edge Architecture Specification] | |
| TCN | permanent | | [RFC 2295: Transparent Content Negotiation in HTTP] | |
| TE | permanent | | [RFC 9110, Section 10.1.4: HTTP Semantics] | |
| Timeout | permanent | | [RFC 4918: HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)] | |
| Timing-Allow-Origin | provisional | | [Resource Timing Level 1] | |
| Topic | permanent | | [RFC 8030, Section 5.4: Generic Event Delivery Using HTTP Push] | |
| Traceparent | permanent | | [Trace Context] | |
| Tracestate | permanent | | [Trace Context] | |
| Trailer | permanent | | [RFC 9110, Section 6.6.2: HTTP Semantics] | |
| Transfer-Encoding | permanent | | [RFC 9112, Section 6.1: HTTP Semantics] | |
| TTL | permanent | | [RFC 8030, Section 5.2: Generic Event Delivery Using HTTP Push] | |
| Upgrade | permanent | | [RFC 9110, Section 7.8: HTTP Semantics] | |
| Urgency | permanent | | [RFC 8030, Section 5.3: Generic Event Delivery Using HTTP Push] | |
| URI | obsoleted | | [RFC 2068: Hypertext Transfer Protocol -- HTTP/1.1] | |
| Use-As-Dictionary | permanent | | [RFC 9842, Section 2.1: Compression Dictionary Transport] | |
| User-Agent | permanent | | [RFC 9110, Section 10.1.5: HTTP Semantics] | |
| Variant-Vary | permanent | | [RFC 2295: Transparent Content Negotiation in HTTP] | |
| Vary | permanent | | [RFC 9110, Section 12.5.5: HTTP Semantics] | |
| Via | permanent | | [RFC 9110, Section 7.6.3: HTTP Semantics] | |
| Want-Content-Digest | permanent | | [RFC 9530, Section 4: Digest Fields] | |
| Want-Digest | obsoleted | | [RFC 3230: Instance Digests in HTTP] | Obsoleted by [RFC 9530, Section 1.3: Digest Fields] |
| Want-Repr-Digest | permanent | | [RFC 9530, Section 4: Digest Fields] | |
| Warning | obsoleted | | [RFC 9111, Section 5.5: HTTP Caching] | |
| WWW-Authenticate | permanent | | [RFC 9110, Section 11.6.1: HTTP Semantics] | |
| X-Content-Type-Options | permanent | | [Fetch] | |
| X-Frame-Options | permanent | | [HTML] | |
| * | permanent | | [RFC 9110, Section 12.5.5: HTTP Semantics] | (reserved) |