Standard metadata names

The HTML specification defines the following set of standard metadata names:

• application-name: the name of the application running in the web page.

  Note:

  • Browsers may use this to identify the application. It is different from the <title> element, which usually contain the application name, but may also contain information like the document name or a status.
  • Simple web pages shouldn't define an application-name.
• author: the name of the document's author.
• description: a short and accurate summary of the content of the page. Several browsers, like Firefox and Opera, use this as the default description of bookmarked pages.
• generator: the identifier of the software that generated the page.
• keywords: words relevant to the page's content separated by commas.
• referrer: controls the HTTP Referer header of requests sent from the document:

  Values for the content attribute of <meta name="referrer">

  no-referrer	Do not send a HTTP Referer header.
  origin	Send the origin of the document.
  no-referrer-when-downgrade	Send the full URL when the destination is at least as secure as the current page (HTTP(S)→HTTPS), but send no referrer when it's less secure (HTTPS→HTTP). This is the default behavior.
  origin-when-cross-origin	Send the full URL (stripped of parameters) for same-origin requests, but only send the origin for other cases.
  same-origin	Send the full URL (stripped of parameters) for same-origin requests. Cross-origin requests will contain no referrer header.
  strict-origin	Send the origin when the destination is at least as secure as the current page (HTTP(S)→HTTPS), but send no referrer when it's less secure (HTTPS→HTTP).
  strict-origin-when-cross-origin	Send the full URL (stripped of parameters) for same-origin requests. Send the origin when the destination is at least as secure as the current page (HTTP(S)→HTTPS). Otherwise, send no referrer.
  unsafe-URL	Send the full URL (stripped of parameters) for same-origin or cross-origin requests.

  Note:

  • Dynamically inserting <meta name="referrer"> (with document.write() or appendChild()) makes the referrer behavior unpredictable.
  • When several conflicting policies are defined, the no-referrer policy is applied.
• theme-color: indicates a suggested color that user agents should use to customize the display of the page or of the surrounding user interface. The content attribute contains a valid CSS <color>. The media attribute with a valid media query list can be included to set the media the theme color metadata applies to.
• color-scheme: specifies one or more color schemes with which the document is compatible. The browser will use this information in tandem with the user's browser or device settings to determine what colors to use for everything from background and foregrounds to form controls and scrollbars. The primary use for <meta name="color-scheme"> is to indicate compatibility with—and order of preference for—light and dark color modes. The value of the content property for color-scheme may be one of the following:

  normal

  The document is unaware of color schemes and should be rendered using the default color palette.

  [light | dark]+

  One or more color schemes supported by the document. Specifying the same color scheme more than once has the same effect as specifying it only once. Indicating multiple color schemes indicates that the first scheme is preferred by the document, but that the second specified scheme is acceptable if the user prefers it.

  only light

  Indicates that the document only supports light mode, with a light background and dark foreground colors. By specification, only dark is not valid, because forcing a document to render in dark mode when it isn't truly compatible with it can result in unreadable content; all major browsers default to light mode if not otherwise configured.

  For example, to indicate that a document prefers dark mode but does render functionally in light mode as well:

  html

  <meta name="color-scheme" content="dark light" />
  

  This works at the document level in the same way that the CSS color-scheme property lets individual elements specify their preferred and accepted color schemes. Your styles can adapt to the current color scheme using the prefers-color-scheme CSS media feature.

The CSS Device Adaptation specification defines the following metadata name:

• viewport: gives hints about the size of the initial size of the viewport.

  Values for the content of <meta name="viewport">

  Value	Possible subvalues	Description
  width	A positive integer number, or the text device-width	Defines the pixel width of the viewport that you want the website to be rendered at.
  height	A positive integer, or the text device-height	Defines the height of the viewport. Not used by any browser.
  initial-scale	A positive number between 0.0 and 10.0	Defines the ratio between the device width (device-width in portrait mode or device-height in landscape mode) and the viewport size.
  maximum-scale	A positive number between 0.0 and 10.0	Defines the maximum amount to zoom in. It must be greater or equal to the minimum-scale or the behavior is undefined. Browser settings can ignore this rule and iOS10+ ignores it by default.
  minimum-scale	A positive number between 0.0 and 10.0	Defines the minimum zoom level. It must be smaller or equal to the maximum-scale or the behavior is undefined. Browser settings can ignore this rule and iOS10+ ignores it by default.
  user-scalable	yes or no	If set to no, the user is not able to zoom in the webpage. The default is yes. Browser settings can ignore this rule, and iOS10+ ignores it by default.
  viewport-fit	auto, contain or cover	The auto value doesn't affect the initial layout viewport, and the whole web page is viewable. The contain value means that the viewport is scaled to fit the largest rectangle inscribed within the display. The cover value means that the viewport is scaled to fill the device display. It is highly recommended to make use of the safe area inset variables to ensure that important content doesn't end up outside the display.

  Warning:

  Disabling zooming capabilities by setting user-scalable to a value of no prevents people experiencing low vision conditions from being able to read and understand page content.

  • MDN Understanding WCAG, Guideline 1.4 explanations
  • Understanding Success Criterion 1.4.4 | W3C Understanding WCAG 2.0

The WHATWG Wiki MetaExtensions page contains a large set of non-standard metadata names that have not been formally accepted yet; however, some of the names included there are already used quite commonly in practice — including the following:

• creator: the name of the creator of the document, such as an organization or institution. If there are more than one, several <meta> elements should be used.
• googlebot, a synonym of robots, is only followed by Googlebot (the indexing crawler for Google).
• publisher: the name of the document's publisher.
• robots: the behavior that cooperative crawlers, or "robots", should use with the page. It is a comma-separated list of the values below:

  Value	Description	Used by
  index	Allows the robot to index the page (default).	All
  noindex	Requests the robot to not index the page.	All
  follow	Allows the robot to follow the links on the page (default).	All
  nofollow	Requests the robot to not follow the links on the page.	All
  all	Equivalent to index, follow	Google
  none	Equivalent to noindex, nofollow	Google
  noarchive	Requests the search engine not to cache the page content.	Google, Yahoo, Bing
  nosnippet	Prevents displaying any description of the page in search engine results.	Google, Bing
  noimageindex	Requests this page not to appear as the referring page of an indexed image.	Google
  nocache	Synonym of noarchive.	Bing

  Note:

  • Only cooperative robots follow these rules. Do not expect to prevent email harvesters with them.
  • The robot still needs to access the page in order to read these rules. To prevent bandwidth consumption, use a robots.txt file.
  • If you want to remove a page, noindex will work, but only after the robot visits the page again. Ensure that the robots.txt file is not preventing revisits.
  • Some values are mutually exclusive, like index and noindex, or follow and nofollow. In these cases the robot's behavior is undefined and may vary between them.
  • Some crawler robots, like Google, Yahoo and Bing, support the same values for the HTTP header X-Robots-Tag; this allows non-HTML documents like images to use these rules.

• Viewport <meta> tag
• Metadata: the <meta> element in What's in the head? Metadata in HTML