science

List of HTTP header fields

List of HTTP header fields is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand List of HTTP header fields rather than just read about it. In short: This article lists standard and notable non-standard HTTP header fields. A core set of fields is standardized by the Internet Engineering Task Force (IETF) in RFC 9110 and 9111.

Key takeaways

List of HTTP header fields belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect List of HTTP header fields to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of List of HTTP header fields from memory before moving on to harder problems.

Reference excerpt

This article lists standard and notable non-standard HTTP header fields. A core set of fields is standardized by the Internet Engineering Task Force (IETF) in RFC 9110 and 9111. The Field Names, Header Fields and Repository of Provisional Registrations are maintained by the IANA. Additional fields may be defined by a web application. In the past, non-standard header field names were prefixed with X- but this convention was deprecated in June 2012 because of the inconveniences it caused when non-standard fields became standard. An earlier restriction on use of Downgraded- was lifted in March 2013. A few field values can contain comments (i.e. in User-Agent, Server, Via fields), which can be ignored by software. Many field values may contain a quality (q) key-value pair separated by equals sign, specifying a weight to use in content negotiation. For example, a browser may indicate that it accepts information in German or English, with German as preferred by setting the q value for de higher than that of en, as follows: Accept-Language: de; q=1.0, en; q=0.5

Request fields This section lists header fields used in a request.

Standard request fields

A-IM [RFC 3229, permanent] Acceptable instance-manipulations for the request. For example: A-IM: feed

Accept [RFC 9110, permanent] Media type(s) that is/are acceptable for the response. See Content negotiation. For example: Accept: text/html

Accept-Charset [RFC 9110, permanent] Character sets that are acceptable. For example: Accept-Charset: utf-8

Accept-Datetime [RFC 7089, provisional] Acceptable version in time. For example: Accept-Datetime: Thu, 31 May 2007 20:35:00 GMT

Accept-Encoding [RFC 9110, permanent] List of acceptable encodings. See HTTP compression. For example: Accept-Encoding: gzip, deflate

Accept-Language [RFC 9110, permanent] List of acceptable human languages for response. See Content negotiation. For example: Accept-Language: en-US

Access-Control-Request-Method, Access-Control-Request-Headers [permanent] Initiates a request for cross-origin resource sharing with Origin (below). For example: Access-Control-Request-Method: GET

Authorization [RFC 9110, permanent] Authentication credentials for HTTP authentication. For example: Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==

Cache-Control

[RFC 9111, permanent] Used to specify directives that must be obeyed by all caching mechanisms along the request-response chain. Per HTTP/1.1, the no-cache value allows the browser to tell the server and intermediate caches that it wants a fresh version of the resource. In HTTP/1.0, the Pragma: no-cache header field has the same purpose. The behavior of no-cache in a response is not specified yet some user agents support it. HTTP/1.1 specifically warns against relying on this behavior. For example: Cache-Control: no-cache

Connection [RFC 9110, permanent] Control options for the current connection and list of hop-by-hop request fields. Must not be used with HTTP/2. For example: Connection: keep-alive Connection: Upgrade

Content-Digest [RFC 9530, Digest Fields] Content-Digest header enables verification of message content integrity by computing a digest over the literal bytes transmitted in the HTTP message. This digest reflects the content after applying transformations like Content-Encoding, matching exactly what travels across the network.

Content-Encoding [RFC 9110, permanent] The type of encoding used on the data. See HTTP compression. For example: Content-Encoding: gzip

Content-Length [RFC 9110, permanent] The length of the request body in octets (8-bit bytes). For example: Content-Length: 348

Content-MD5 [RFC 1544, 1864, 4021, obsolete] A Base64-encoded binary MD5 sum of the content of the request body. For example: Content-MD5: Q2hlY2sgSW50ZWdyaXR5IQ==

Content-Type [RFC 9110, permanent] The Media type of the body of the request (used with POST and PUT requests). For example: Content-Type: application/x-www-form-urlencoded

Cookie [RFC 2965, 6265, permanent] An HTTP cookie previously sent by the server with Set-Cookie (below). For example: Cookie: $Version=1; Skin=new;

Date [RFC 9110, permanent] The date and time at which the message was originated (in "HTTP-date" format as defined by RFC 9110: HTTP Semantics, section 5.6.7 "Date/Time Formats"). For example: Date: Tue, 15 Nov 1994 08:12:31 GMT

Expect [RFC 9110, permanent] Indicates that particular server behaviors are required by the client. For example: Expect: 100-continue

Forwarded [RFC 7239, permanent] Disclose original information of a client connecting to a web server through an HTTP proxy. For example: Forwarded: for=192.0.2.60;proto=http;by=203.0.113.43 Forwarded: for=192.0.2.43, for=198.51.100.17

From [RFC 9110, permanent] The email address of the user making the request. For example: From: user@example.com

Host [RFC 9110, 9113, permanent] The domain name of the server (for virtual hosting), and the TCP port number on which the server is listening. The port number may be omitted if the port is the standard port for the service requested. Mandatory since HTTP/1.1. If the request is generated directly in HTTP/2, it should not be used. For example: Host: en.wikipedia.org:8080 Host: en.wikipedia.org

HTTP2-Settings [RFC 7540, 9113, obsolete] A request that upgrades from HTTP/1.1 to HTTP/2 MUST include exactly one HTTP2-Settings header field. The HTTP2-Settings header field is a connection-specific header field that includes parameters that govern the HTTP/2 connection, provided in anticipation of the server accepting the request to upgrade. For example: HTTP2-Settings: token64

If-Match [RFC 9110, permanent] Only perform the action if the client supplied entity matches the same entity on the server. This is mainly for methods like PUT to only update a resource if it has not been modified since the user last updated it. For example: If-Match: "737060cd8c284d8af7ad3082f209582d"

If-Modified-Since [RFC 9110, permanent] Allows a 304 Not Modified to be returned if content is unchanged. For example: If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT

If-None-Match [RFC 9110, permanent] Allows a 304 Not Modified to be returned if content is unchanged, see HTTP ETag. For example: If-None-Match: "737060cd8c284d8af7ad3082f209582d"

If-Range [RFC 9110, permanent] If the entity is unchanged, send me the part(s) that I am missing; otherwise, send me the entire new entity. For example: If-Range: "737060cd8c284d8af7ad3082f209582d"

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with List of HTTP header fields

Start with the simplest possible case. Write down what List of HTTP header fields claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to List of HTTP header fields before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about List of HTTP header fields ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of List of HTTP header fields

In research: List of HTTP header fields appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses List of HTTP header fields in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: List of HTTP header fields is common in secondary-school and first-year university syllabi. It links to neighbouring topics Hypertext Transfer Protocol headers, Internet-related lists, so understanding it makes those chapters shorter.
In everyday life: Look for List of HTTP header fields outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study List of HTTP header fields in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what List of HTTP header fields means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain List of HTTP header fields out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is List of HTTP header fields in simple terms?

This article lists standard and notable non-standard HTTP header fields. A core set of fields is standardized by the Internet Engineering Task Force (IETF) in RFC 9110 and 9111.

Why does List of HTTP header fields matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study List of HTTP header fields?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on List of HTTP header fields.