List of HTTP Headers: Definitions, Types, Usage, Syntax, and Directives

List of HTTP Headers contain the security, server, client hint, redirect, and other types of HTTP Headers based on their types, syntaxes, and uses. HTTP Headers are to let web servers serve additional information as a response to an HTTP request or response. The format of the HTTP Headers contains an HTTP Header with case-insensitive form, a “:” and white space for its value. HTTP Headers contain prefixes such as “X-” for the custom proprietary headers. The RFC 6648, RFC 4229, RFC 3229, RFC 2616, and more define the uses and syntax of the HTTP Headers. Every HTTP Header can be seen via a curl command, or from a web browser. The Ianıa Registry Permanent Message Headers contain all of the permanent HTTP Headers.

What is the format of HTTP Headers?

The header fields are transmitted after the request line (in case of a request HTTP message) or the response line (in case of a response HTTP message), which is the first line of a message. Header fields are colon-separated key-value pairs in clear-text string format, terminated by a carriage return (CR) and line feed (LF) character sequence. The end of the header section is indicated by an empty field line, resulting in the transmission of two consecutive CR-LF pairs. In the past, long lines could be folded into multiple lines; continuation lines are indicated by the presence of a space (SP) or horizontal tab (HT) as the first character on the next line. This folding is now deprecated. Below, an example of HTTP Header format can be found.

HTTP-Header: Directive
Second-HTTP-Header: Directive

What are the Field Names for HTTP Headers?

Internet Engineering Task Force (IETF) standardized the field names of the HTTP Headers in RFCs 7235, 7234, 7231, 7233, and 7230. Header field names are case-insensitive, and HTTP 2 made some restrictions for the non-standard field names. The X- prefix was traditionally used to mark non-standard header fields, but this convention was deprecated in June 2012 due to inconveniences it caused when non-standard fields became standard. March 2013 marked the end of an earlier restriction on the use of Downgraded-.

What are the Field Values for HTTP Headers?

Field Values can be used within the Content Negotiations. HTTP Header Field Values can contain an equal sign or a semi-colon. The “q” can be used with an equal sign as a key-value pair. Below, you can see an example of the field value used for HTTP Headers.

Accept-Language: en; q=2.0, en; q=1 

What is the size limit for HTTP Headers?

There is no size limit for HTTP Headers. The HTTP Headers can be many as possible, and they can belong as much as they can. But, because of the page loading performance issues, and security reasons, the proxy servers, and the web servers limit the size of HTTP Headers. For instance, Apache Servers limits the HTTP Header size is 8,190 bytes and 100 HTTP Headers.

What are the types of HTTP Headers?

There are six types of HTTP Headers. The types of HTTP Headers are listed below.

• Response HTTP Headers
• Representation HTTP Headers
• Payload HTTP Headers
• Request HTTP Headers
• End-to-end HTTP Headers
• Hop-by-hop HTTP Headers

1. HTTP Request Headers and Fields

The Request HTTP Headers can be seen with their descriptions, examples, status, and RFC Document references in the HTTP Request Headers Table below.

The common non-standard Request HTTP Headers can be seen with their descriptions and examples in the Non-standard HTTP Request Headers Table below.

2. HTTP Response Headers and Fields

The standard common HTTP Response Headers can be seen with their descriptions, examples, status, and RFC Document references in the standard HTTP Response Headers Table below.

The non-standard common HTTP Response Headers can be seen with their descriptions, examples, status, and RFC Document references in the non-standard HTTP Response Headers Table below.

3. Representation Headers

A representation HTTP Header represents a resource that is sent within an HTTP message body. A representation of a source can vary based on the resource type. Representations can be in different forms, and formatted as XML, or JSON. Some of the representation headers are below.

• Content-type
• Content-Encoding
• Content-Language
• Content-Location

4. Payload Headers

A Payload HTTP Header contains the payload data for constructing the representation of the resource. The length of the resource, encoding, and integrity information can be passed with payload headers. Some of the Payload HTTP Headers are listed below.

• Content-length
• Content-Range
• Trailer
• Transfer-Encoding

What are the Lists of HTTP Headers?

The lists of the HTTP Headers involve the HTTP Header Types with their purposes and contexts. The lists of the HTTP Headers are below.

• Authentication HTTP Headers
• Caching HTTP Headers
• Device Client Hints
• Network Client Hint HTTP Headers
• Conditional HTTP Headers
• Connection Management HTTP Headers
• Content Negotiation HTTP Headers
• Controls HTTP Headers
• Cookies HTTP Head
• CORS HTTP Headers
• Downloads HTTP Headers
• Message Body Information HTTP Head
• Proxies HTTP Headers
• Redirect HTTP Headers
• Request Context HTTP Headers
• Response Context HTTP Headers
• Range Requests HTTP Headers
• 16. Security HTTP Headers
• 17. HTTP Public Key Pinning (HPKP) HTTP Headers
• 18. Fetch Metadata Request HTTP Headers
• Server-sent Events HTTP Headers
• Transfer Coding HTTP Headers
• WebSockets HTTP Headers
• Other HTTP Headers

All of the HTTP Headers, their directives, syntaxes, and rules can be read with their purposes and usage from the next sections.

1. Authentication HTTP Headers

Authentication HTTP Headers are used for proxy and webserver authentication. They help with using a proxy server with only certain authentication information. Web servers are able to communicate with the user-agent and requester based on this information. The authentication response headers are listed below.

• WWW-Authenticate: Determines the authentication method for a resource.
• Authorization: contains the password, username, and other authentication user-agent information within the web server.
• Proxy-Authenticate: Defines the authentication for a proxy server for a resource.
• Proxy-Authorization: Defines the authentication for the entire proxy web server.

Authentication HTTP Headers should be used if a web server or proxy server is used by a developer for private web development or data storage purposes.

2. Caching HTTP Headers

Caching HTTP Headers are useful for caching resources that are necessary for a web page. Caching HTTP Headers can be used for images, javascript files, CSS files, font files, and other related resources such as manifest files. The caching HTTP Headers are listed belowç

• Age
• Cache-control
• Clear-Site-Data
• Expires
• Pragma
• Warning

Using the caching HTTP HEders is important for especially providing a better page loading experience and timing.

2. Client Hint HTTP Headers

Client Hint HTTP Headers are to provide information related to the network and device conditions of the client. It is important to sweb servers to optimize them based on the clients’ conditions. There are two types of Client Hint HTTP Headers, these are Device Client HTTP Headers and Network client HTTP Headers.

The most important and fundamental client HTTP Headers are listed below.

• Accept-CH: only can be used within a TLS Connection. It can request the viewport width and device-width of the user.
• Accept-CH-Lifetime: it requests the client hints for a lifetime for the further requests.

3. Device Client Hints

Device Client Hints are for providing information related to the client’s device.

• Content-DPR: it is to provides an image device pixel ratio for choosing an image resource based on the DPR hint.
• Device-Memory: It is part of Device Memory API. It is for learning the RAM memory of the user’s device.
• DPR: It is for learning the client’s devices’ pixel ratio. It will affect the CSS Pixel position-related commands.
• Viewport-Width: Layout with CSS Pixels can be provided with Viewport-Width.
• Width: It represents the intrinsic size of an image directly.

4. Network Client Hint HTTP Headers

Network Client Hint HTTP Headers are for providing information related to the client’s network conditions. Below, you can see the Network Client Hint HTTP Headers as listed.

• Downlink: it is for learning the range of bandwidth of the client’s internet connection in the Mbps unit. Downlink HTTP Header is a part of the Network Information API.
• ECT: it stands for effective connection type or network profile. It is part of the Network Information API. It learns the latency of the connection for the webserver.
• RTT: It is related to the Round Trip Time. It is part of the Network Information API.
• Save-Data: It shows whether the user wants to save the size and cost while surfing the web or not.

5. Conditional HTTP Headers

Conditional HTTP Headers change the resource’s HTTP Status Code based on the conditions. Conditional HTTP Headers are useful for adaptive serving and the caching HTTP Headers’ implementation. Conditional HTTP Headers are listed below.

• Last-Modified: It is to compare the several different versions of the resource that is requested. It helps a web server to make a change for the resource, based on the last modification date. It is similar to E-tag but less accurate. If-Modified-Since and If-Unmodified-Since can be used with Last-Modified.
• ETag: E-tag is a unique identification string that defines a resource. If-match and If-None-Match can be used with E-tag Conditional HTTP Headers.
• If-Match: it is for ETag value. If the Etag value of the client and the webserver matches, the resource will be served as it is.
• If-None-Match: it is for Etag value. If the Etag HTTP Header value doesn’t match between the web server and the client, the cache will be updated.
• If-Modified-Since: It is used with Last-Modified. If a resource is updated after a certain date, it can be refreshed within the cache.
• If-Unmodified-Since: It is used with a Last-Modified HTTP Header value. If a resource is unmodified since a certain date, the resource won’t be updated within the browser cache.
• Vary: It is used for matching the cached version with the requested version.

The conditional HTTP Headers are important to learn for web browsers’ working principle, and HTTP Caching Strategies.

4. Connection Management HTTP Headers

Connection Management HTTP Headers control the connection of the request. Whether to keep a connection alive or how long it should stay life can be determined with Connection Management HTTP Headers. The Connection Management HTTP Headers are listed below.

• Connection: it is to determine whether the connection should stay alive or not after transferring a resource.
• Keep-Alive: it is to control how long a connection should stay valid and open after the transaction of a resource from a web server to the web browser.

Connection Management HTTP Headers are important for adjusting the server overload, and the response time quality. Using the wrong connection management from a web server configuration can affect the Time to First Byte (TTFB).

5. Content Negotiation HTTP Headers

Content Negotiation HTTP Headers are to provide information for the encoding of the document, the language of the document, and what information will be accepted in terms of its type by the webserver. The Content Negotiation HTTP Headers are listed below.

• Accept: It determines what types of data and resources can be sent back to the webserver.
• Accept-Encoding: It represents the compression algorithm that has been used by the webserver for sending information to the web browser.
• Accept-Language: It is to provide human language information the webserver is expected to send back, and it is an optional hint, not a command that can overwrite the preference of the web browser user.

The content negotiation HTTP Headers are especially important for using a proper server-side compression algorithm such as Brotli for better page speed.

6. Controls HTTP Headers

Control HTTP Headers are to determine how the expectations will be performed by the server while handling a request.

• Expect: It is to provide conditions for certain types of situations. If the Content-Length is too much, and Expect HTTP Header can change the HTTP Status Code based on this.
• Max-Forwards: it is to be used within the TRACE method to limit the number of requests from an IP Address. It helps a web server to protect itself from an excessive amount of requests from a proxy.

The Controls HTTP Headers are important to create different conditional webserver behavior variations.

7. Cookies HTTP Headers

Cookies HTTP Headers are to use the cookies within the HTTP Headers. It can be used for sending cookies or receiving cookies from the web servers. The list of the Cookies HTTP Headers is below.

• Cookie: It contains all of the cookies that are determined with the Set-Cookie HTTP Header previously.
• Set-Cookie: Set-Cookie is to provide cookies from the web server to the user agent.
• Cookie2: it is to provide the obsolete cookies to the user-agent.
• Set-Cookie2: it is to send the obsolete cookies from the web server to the web browser.

The Cookies HTTP Headers are important to use for protecting the users’ privacy, and security while providing a better user experience.

8. CORS HTTP Headers

CORS HTTP Headers are related to Web Security. CORS HTTP Headers are a part of the Security-related HTTP Headers. Cross-Origin Resource Sharing (CORS) is HTTP-header based system to provide a request and response policy between the different origins. The list of the CORS HTTP Headers is below.

• Access-Control-Allow-Origin: Access-Control-Allow-Origin is to determine whether the response will be shared with third-party origins or not.
• Access-Control-Allow-Credentials: Access-Control-Allow-Credentials is to determine whether the response to the request will be exposed if the credentials flag is used with True value.
• Access-Control-Allow-Headers: Access-Control-Allow-Headers is to determine which HTTP Headers can be used for the actual request.
• Access-Control-Allow-Methods: Access-Control-Allow-Methods is to determine which methods can be used for the response.
• Access-Control-Expose-Headers: Access-Control-Expose-Headers is to determine whether the HTTP Response headers will be exposed or not.
• Access-Control-Max-Age: The Access-Control-Max-Age is to determine how long the results for a preflight request will be cached.
• Access-Control-Request-Headers: The Access-Control-Request-Headers is to let a web server which request headers will be used for an actual request.
• Access-Control-Request-Method: Access-Control-Request-Method is to provide the information of which HTTP Method will be used for the actual request.
• Origin: The Origin is let a web server know where a fetch request is originated from.
• Timing-Allow-Origin: The Timing Allow-Origin is to specify origins that are able to see the time attributes via Resource Timing API. If it is not set, the values will be zero.

The CORS HTTP Headers are important for determining a communication between the web browser and the web server for preflight requests.

9. Downloads HTTP Headers

The downloads HTTP Header is only the “Content-Disposition”. The Content-Disposition is to provide a “Save As” dialog within the browser. It determines whether the content should be displayed inline, or it should be handled normally such as a download action.

10. Message Body Information HTTP Headers

The Message Body Information HTTP Headers are to determine the length, type, encoding, location, and language of the response body. It includes the information for the web page in terms of its characteristics. The list of Message-Body HTTP Headers is below.

• Content-Length: Content-Length is to provide the length of the resource in decimal numbers of bytes.
• Content-Type: Content-Type is to provide the media type of the resource that will be sent.
• Content-Encoding: Content-Encoding is to provide the compression algorithm of the resource.
• Content-Language: Content-Language is to provide the information of human language for the audience.
• Content-Location: Content-Location is to provide an alternate location for the returned data.

The Message Body Information HTTP Headers are important to give the features of a resource within a web page.

11. Proxies HTTP Headers

The Proxies HTTP Headers are to provide information for the proxy servers and their behaviors. The list of Proxies HTTP Headers is below.

• Forwarded: Forwarded Proxies HTTP Header is to provide information client-facing side of the proxy server when a proxy server information is lost and changed if the proxy is in the path of the request.
• X-Forwarded-For: X-Forwarded-For Proxies HTTP Header is to identify the originating IP Address.
• X-Forwarded-Host: X-Forwarded-Host HTTP Header is to provide information of the host requested for a client used to connect to a proxy or a load balancer.
• X-Forwarded-Proto: The X-Forwarded-Proto Proxies HTTP Header is to specify the protocol between HTTP and HTTPS to connect a proxy or load balancer.
• Via: The Via Proxies HTTP Header is to provide information for the forward and reverse proxies that can appear in the request and response headers.

The Proxies HTTP Headers are important to manage a Proxy Server.

12. Redirect HTTP Headers

There is only one Redirect HTTP Header which is “Location”. Location Redirect HTTP Header refers to the URL that a web page will be redirected.

13. Request Context HTTP Headers

The Request Content HTTP Headers are to provide context around the request for the webserver. The list of request context HTTP Headers can be seen below.

• Form: The From Request Context HTTP Header is to provide an internet email address to a web user who controls the user-agent.
• Host: Host Request Context HTTP Header is to specify the domain name of the webserver, and TCP Port Number.
• Referer: The Referrer Request Context HTTP Header is to provide which web page URL is a referrer for the next web page URL that is navigated.
• Referrer-Policy: Referrer-Policy Request Context HTTP Header is to determine what referrer information will be sent.
• User-Agent: User-Agent Request Context HTTP Header is to provide a string that reflects the web browser, device, internet connection, application type, the operation system of the web browser user.

The Request Context HTTP Headers are important to perform a healthy log analysis for the web servers and protect the web browser user privacy.

14. Response Context HTTP Headers

The Response Context HTTP Headers is to provide the information related to the Response of the webserver. The list of the response context HTTP Headers is below.

• Allow: Allow Response Context Header is to provide lists of the HTTP Request Methods that can be used for a resource from the webserver.
• Server: Server Response Context HTTP Header is to server the information related to the webserver.

15. Range Requests HTTP Headers

Range Requests HTTP Headers can be used for providing information related to the range requests. The list of the range HTTP Headers is below.

• Accept-Ranges: Accept-Ranges HTTP Header is to provide information related to the range request’s acceptance situation. It specifies the unit of the range request.
• Range: Range Range Request HTTP Header is to provide information for the document that the server will return.
• If-Range: If-Range Range Request HTTP Header is to provide information for conditional range requests. It will be performed based on the given Etag, or the date.
• Content-Range: The Content-Range Range HTTP Request is to provide information for the related range request’s size.

The Range HTTP Requests Headers are useful to manage range requests properly.

16. Security HTTP Headers

Security HTTP Headers are to provide information related to the security needs of a response or the request. Security-related HTTP Headers are to protect the privacy of web users while protecting them from cybersecurity issues and vulnerabilities. The list of Security HTTP Headers can be seen below.

• X-Frame-Options: X-Frame-Options Security HTTP Header is to provide protection against the clickjacking
• X-Permitted-Cross-Domain-Policies: X-Permitted-Cross-Domain-Policies Security HTTP Header is to specify if a cross-domain policy file is allowed or not. The file can define the rules for the specific resources’ types share conditions and policy. X-Permitedd-Cross-Domain-Policies is related to the Cross-Domain Policy File Specification.
• X-Powered-By: X-Powered-By Security HTTP Header is to provide information related to the hosting environments, and the frameworks that are used for the website.
• X-XSS-Protection: X-XSS-Protection Security HTTP Header is to provide protection against the XSS Attacks.
• Cross-Origin-Embedder-Policy: Cross-Origin-Embedder Security HTTP Header is to declare an embedded policy for the resources.
• Cross-Origin-Opener-Policy: Cross-Origin-Opener-Policy is to prevent third-party origins from opening, and controlling a window for the previous window.
• Content-Security-Policy: Content Security Policy Security HTTP Header is to control which resource type will be requested from which server.
• Content-Security-Policy-Report-Only: Content-Security-Policy-Report-Only: Security HTTP Header is to provide a JSON HTTP Post for reporting the violations.
• Expect-CT: Expect-CT Security HTTP Header is to provide information for the timestamp of the TLS Certificate. Certificate Transparency and CT Logs are related to the Expect-CT.
• Feature-Policy: Feature-Policy SEcurity HTTP Header is to provide information for the mechanism of allowing, or denying a web browser feature.
• Origin-Isolation: Origin-Isolation Security HTTP Header is to provide a mechanism for a web application for isolating their origins.
• Strict-Transport-Security (HSTS): Strict-Transport-Security HTTP Header is to provide a forceful 307 Redirection to the HTTPS version of a website.
• Upgrade-Insecure-Requests: Upgrade-Insecure-Requests Security HTTP Header is to force a web browser to use always HTTPS if the request is made to the HTTP.
• X-Content-Type-Options: X-Content-Type-Options are to prevent MIME Snıffing cybersecurity vulnerability.
• X-Download-Options: X-Download-Options are to prevent phishing attacks.

The HTTP Security Response Headers are critical for search engine optimization, user security, and web server security. To learn more about the HTTP Security Response Headers, read the related guide.

17. HTTP Public Key Pinning (HPKP) HTTP Headers

The HTTP Pubic Key Pinning (HPKP) HTTP Headers are important to provide information related to the

• Public-Key-Pins
• Public-Key-Pins-Report-Only

18. Fetch Metadata Request HTTP Headers

The Fetch Metadata Request Headers are to provide information for the context of the request. A web server can give different decisions based on the fetch metadata request headers.

• Sec-Fetch-Sites: Sec-Fetch-Sites Fetch Metadata Request HTTP Header is to determine the relationship between a request’s origin, and its target. Since, it is a structured Header, it can have values with “cross-site”, “same-origin”, “same-site”, and “none”.
• Sec-Fetch-Mode: Sec-Fetch-Mode Fetch Metadata Request HTTP Header is to provide information related to the mode of the request such as “cors”, “navigate,” “no-cors”, “same-origin”, “websocket”.
• Sec-Fetch-User: Sec-Fetch-user Fetch Metadata Request HTTP Header is to provide information related to the navigation event’s request. If the navigation is triggered by the user the value of the Sec-Fetch-user will be “?1”, if it is not triggered by the user, it will be “?1”.
• Sec-Fetch-Dest: Sec-Fetch-Dest Fetch Metadata Request HTTP Headers is a header that indicates the request’s destination to a server. It is a structured HTTP Header that contains tokens with the values “audio”, “audioworklet”, “empty”, “sharedworker”, “style”, “video”, “xlst”, “report”, “serviceworker”, “embed.

The Fetch Metadata Request HTTP Headers are prominent to see the characteristics of the Fetch Requests.

19. Server-sent Events HTTP Headers

Server-sent Events HTTP Headers are prominent to provide information related to the server events. There are 5 different Server-sent Events HTTP Headers. The list of Server-sent Events HTTP Headers is below.

• Last-Event-ID: The Last-Event-ID Server-sent HTTP Haeder is to provide information for automatically reconnect requets if the network is interrupted.
• NEL: NEL Server-sent Events HTTP Headers is to configure loggings for the network requests.
• Ping-From: Ping-From Server-sent Events HTTP Header is to provide a ping information source.
• Ping-To: Ping-To Server-sent Events HTTP Headers it o provide a ping information target.
• Report-To: Report-To Server-sent Events HTTP Header is to provide a reporting endpoint.

Server-Sent Events HTTP Headers are rarely used, and they are useful for controlling server-sent events.

20. Transfer Coding HTTP Headers

Transfer-Encoding HTTP Headers is to determine the encoding of a resource transfer to a web user. There are three Transfer Coding HTTP Headers. The Transfer Coding HTTP Header list is below.

• Transfer-Encoding: Transfer-Encoding Transfer Coding HTTP Header is to specify the encoding of the safely transferred resource.
• TE: TE Transfer-Encoding HTTP Header is to make transfer encoding clear to the user-agent.
• Trailer: Trailer Transfer-Encoding HTTP Header is to determine the additional fields for the sender’s message.

Transfer Coding HTTP Headers are related to the hop-by-hop headers.

21. WebSockets HTTP Headers

WebSockets HTTP Headers are used for the WebSockets. WebSockets are used for sending data and receiving data. A WebSocket can create two-way interactive communication between a web browser user and a web server. Thus, WebSocket HTTP Headers are prominent to improve the communication between users and the web server in an interactive and event-based way.

• Sec-WebSocket-Key: Sec-WebSocket-Key is to prove that the client has taken the web server’s key for creating the WebSockets connection.
• Sec-WebSocket-Extensions: Sec-WebSocket-Extensions WebSockets HTTP Header is to open handshake.
• Sec-WebSocket-Accept: Sec-WebSocket-Accept WebSockets HTTP Header is to initiate a WebSocket connection.
• Sec-WebSocket-Protocol: Sec-WebSocket-Protocol WebSocket HTTP Header is to choose a protocol between HTTP and HTTPS.
• Sec-WebSocket-Version: Sec-WebSocket-Version WebSocket HTTP Header is to specify the version of the web socket.

WebSockets HTTP Headers are relevant to the WebSocket API.

22. Other HTTP Headers

Other HTTP Headers are HTTP Headers that are not classified under a contextual group. They can be related to the server push methods, or alternate methods to reach out to a server. In this context, there are 22 different HTTP Headers. The other HTTP Headers are listed below.

• Accept-Push-Policy: Accept-Push-Policy refers to a specific server push policy.
• Accept-Signatures: Accept-Signatures is to provide a signature that can be accepted.
• Alt-Svc: Alt-SVC is to provide a list of alternate access methods to a server.
• Date: Date HTTP Header is to provide a date for the message that is created.
• Early-Data: Early-Data HTTP Header is to provides information on the data that is conveyed in TLS.
• Large-Allocation: Large-Allocation HTTP Header is to provide signals that the webserver will perform a large load for the web browser.
• Link: The link entity-header field provides a link declaration that is equal to the Link HTML Element.
• Push-Policy: Push Policy HTTP Header provides a patterned behavior for performing a push request.
• Retry-After: Retry-After HTTP Header Specifies how long a user-agent should wait to make a new request.
• Signature: Signature Header field caries a signal for exhchange of information.
• Signed-Headers: Signed Headers HTTP Header contains fileds to include within a signature. Signed-Headers is important for the Signed HTTP Exchanges.
• Server-Timing: Server-Timing HTTP Header identifies a communication metric, and description for the request-response cycle.
• Service-Worker-Allowed: Service-Worked-Allowed is used to specify the restricted paths for the Service Workers. Now, it can be contained within the service worker’s itself.
• SourceMap: SourceMap HTTP Header is to provide a source URL for the compiled JS code during the debug process.
• Upgrade: The Upgrade HTTP Header is to provide an increment for the HTTP Protocol. It is specified in the RFC 7230, section 6.7.
• X-DNS-Prefetch-Control: X-DNS-Prefetch-Control is HTTP Header to control whether the web browser will be able to perform DNS Resolution or not.
• X-Firefox-Spdy: X-Firefox-Spdy HTTP Header is obsolete, and it had been used for SPDY check within Firefox.
• X-Pingback: X-Pingback HTTP Header is to provide a linkback possibility.
• X-Requested-With: X-Requested-With is a HTTP Header for making clear that Ajax Libraries, or some other JQuery and Dojo Libraries are requested with XMLHttpRequest not by clicking a standard hyperlink.
• X-Robots-Tag: X-Robots-Tag is prominent to SEO, and controlling other crawlers. X-Robots-Tag is to provide information for crawlers to whether the URL should be crawled or not.
• X-UA-Compatible: X-UA-Compatible HTTP Header is prominent to determine which document mode will be used by the Internet Explorer.

What are the other classification methods of HTTP Headers?

The HTTP Headers can be grouped as below.

• Response HTTP Headers
• Representation HTTP Headers
• Payload HTTP Headers
• Request HTTP Headers
• End-to-end HTTP Headers
• Hop-by-hop HTTP Headers

Until now, the Response HTTP Headers, Payload HTTP Headers, Representation HTTP Headers, Request HTTP Headers are processed. The next section will explain the End-to-end HTTP Headers and the Hop-by-hop HTTP Headers.

1. End-to-end HTTP Headers

If you are sending a request, these headers must be sent to the server, and if you are sending a response, they must be sent to the client. Caches must store these headers and intermediate proxies must retransmit them without modification.

2. Hop-by-hop HTTP Headers

Only a single transport-level connection can benefit from these headers, and they should not be cached or retransmitted. Connection headers may only be set for hop-by-hop headers.

What are the HTTP Headers that are listed in IANA Registry?

The HTTP Headers that are listed in the IANA Registry can be seen in the table below with their RFC Reference Document, Status, Protocol, and Header Field Name.

What are the IANA HTTP Headers that are proposed as New HTTP Headers?

The IANA HTTP Headers that are proposed as New HTTP Headers by IANA are in the table below with their status, reference RFC Document, and protocol.

Why is Web Browser important for HTTP Headers?

The main importance of a web browser for HTTP Headers is that a user agent uses a web browser for making a request to a web server. A web browser is an application for using websites with a graphical interface. Thus, a web browser will request resources, download, and render them for creating the web page for the web browser user. An HTTP Header can change how a web browser behaves, and the request HTTP Headers will be delivered from a web browser to the webserver. A web browser’s default request HTTP headers can be changed from its settings for different purposes. The importance of the relation between the HTTP Headers and the web browsers is prominent for understanding how the web works.

Why is Web Server is important for HTTP Headers?

A web server is important for HTTP Headers because a web server sends the HTTP Headers to the web browser user which is a user-agent. A web server can be configured for different HTTP Header usage based on its purpose. Web servers are prominent for web browsers since they send the resources that the browser will render and load. HTTP Headers control the communication between the web browsers and the web servers. A response HTTP Header from a web server will be created based on the request HTTP Header from a web browser. Thus, web servers are a prominent part of the HTTP Headers’ functionality.

Why is a Website important for HTTP Headers?

A website is stored within a web server and served to a web browser via HTTP Headers. A website and its web pages can be served differently based on the HTTP Headers. A website can have different website segments that contain different web pages. In this context, a website and its web pages will be served with certain HTTP Headers. For arranging the cache, security, and content negotiation between the web browser and the web server, the HTTP Headers will be used. HTTP Headers are prominent for websites in terms of conveying the websites to the specific web browser which represents a user agent for the requestor.

Last Thoughts on HTTP Headers and Holistic SEO

The HTTP Headers are prominent to determine which message will be passed from web user to web server, and from web server to the user-agent. The HTTP Headers involve different contexts and groups according to their purposes and usage methodologies. From different HTTP Status Codes to the redirection methods, an HTTP Header can signal multiple-meaning related to the software of the web server, or the encoding of the resource. HTTP Headers can be used for making the web page loading performance better or improving the web page security. Whether it is related to the web page security, or speed, and web server efficiency, HTTP Headers are prominent for SEO. Holistic SEO involves every vertical of SEO efforts. HTTP Headers are related to SEO, UX, and web development in the context of coding. In this context, knowing about HTTP Headers are prominent for an SEO to manage the web development teams for better HTTP Cache Strategies, web security precautions, and web server response efficiency.

The HTTP Header Guide will be updated over time.

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Koray Tuğberk GÜBÜR

Owner and Founder at Holistic SEO & Digital

Koray Tuğberk GÜBÜR is the CEO and Founder of Holistic SEO & Digital where he provides SEO Consultancy, Web Development, Data Science, Web Design, and Search Engine Optimization services with strategic leadership for the agency’s SEO Client Projects. Koray Tuğberk GÜBÜR performs SEO A/B Tests regularly to understand the Google, Microsoft Bing, and Yandex like search engines’ algorithms, and internal agenda. Koray uses Data Science to understand the custom click curves and baby search engine algorithms’ decision trees. Tuğberk used many websites for writing different SEO Case Studies. He published more than 10 SEO Case Studies with 20+ websites to explain the search engines. Koray Tuğberk started his SEO Career in 2015 in the casino industry and moved into the white-hat SEO industry. Koray worked with more than 700 companies for their SEO Projects since 2015. Koray used SEO to improve the user experience, and conversion rate along with brand awareness of the online businesses from different verticals such as retail, e-commerce, affiliate, and b2b, or b2c websites. He enjoys examining websites, algorithms, and search engines.

Latest posts by Koray Tuğberk GÜBÜR (see all)

• SEO for Casino Websites: A SEO Case Study for the Bet and Gamble Industry - February 5, 2024
• Semantic HTML Elements and Tags - January 15, 2024
• What is Interaction to Next Paint (INP), and How to Optimize It - December 7, 2023