chrome.declarativeWebRequest

Description
Note: this API is currently on hold, without concrete plans to move to stable. Use the chrome.declarativeWebRequest API to intercept, block, or modify requests in-flight. It is significantly faster than the chrome.webRequest API because you can register rules that are evaluated in the browser rather than the JavaScript engine, which reduces roundtrip latencies and allows higher efficiency.
Permissions
declarativeWebRequest
Availability
Beta and Dev channels only.

Manifest #

You must declare the "declarativeWebRequest" permission in the extension manifest to use this API, along with host permissions.

{
  "name": "My extension",
  ...
  "permissions": [
    "declarativeWebRequest",
    "*://*/*"
  ],
  ...
}

Note that certain types of non-sensitive actions do not require host permissions:

CancelRequest
IgnoreRules
RedirectToEmptyDocument
RedirectToTransparentImage

The SendMessageToExtension action requires host permissions for any hosts whose network requests you want to trigger a message.

All other actions require host permissions to all URLs.

As an example, if "*://*.google.com/*" is the only host permission an extension has, then such an extension may set up a rule to

cancel a request to "http://www.google.com" or "http://anything.else.com"
send a message when navigating to "http://www.google.com" but not to "http://something.else.com"

The extension cannot set up a rule to redirect "http://www.google.com" to "http://mail.google.com".

Rules #

The Declarative Web Request API follows the concepts of the Declarative API. You can register rules to the chrome.declarativeWebRequest.onRequest event object.

The Declarative Web Request API supports a single type of match criteria, the RequestMatcher. The RequestMatcher matches network requests if and only if all listed criteria are met. The following RequestMatcher would match a network request when the user enters "http://www.example.com" in the URL bar:

var matcher = new chrome.declarativeWebRequest.RequestMatcher({
  url: { hostSuffix: 'example.com', schemes: ['http'] },
  resourceType: ['main_frame']
});

Requests to "https://www.example.com" would be rejected by the RequestMatcher due to the scheme. Also all requests for an embedded iframe would be rejected due to the resourceType.

Note: All conditions and actions are created via a constructor as shown in the example above.

In order to cancel all requests to "example.com", you can define a rule as follows:

var rule = {
  conditions: [
    new chrome.declarativeWebRequest.RequestMatcher({
      url: { hostSuffix: 'example.com' } })
  ],
  actions: [
    new chrome.declarativeWebRequest.CancelRequest()
  ]
};

In order to cancel all requests to "example.com" and "foobar.com", you can add a second condition, as each condition is sufficient to trigger all specified actions:

var rule2 = {
  conditions: [
    new chrome.declarativeWebRequest.RequestMatcher({
      url: { hostSuffix: 'example.com' } }),
    new chrome.declarativeWebRequest.RequestMatcher({
      url: { hostSuffix: 'foobar.com' } })
  ],
  actions: [
    new chrome.declarativeWebRequest.CancelRequest()
  ]
};

chrome.declarativeWebRequest.onRequest.addRules([rule2]);

Note: You should always register or unregister rules in bulk rather than individually because each of these operations recreates internal data structures. This re-creation is computationally expensive but facilitates a very fast URL matching algorithm for hundreds of thousands of URLs. The Performance section of the Events API provides further performance tips.

Evaluation of conditions and actions #

The Declarative Web Request API follows the Life cycle model for web requests of the Web Request API. This means that conditions can only be tested at specific stages of a web request and, likewise, actions can also only be executed at specific stages. The following tables list the request stages that are compatible with conditions and actions.

Request stages during which condition attributes can be processed.
Condition attribute	onBeforeRequest	onBeforeSendHeaders	onHeadersReceived	onAuthRequired
url	✓	✓	✓	✓
resourceType	✓	✓	✓	✓
contentType			✓
excludeContentType			✓
responseHeaders			✓
excludeResponseHeaders			✓
requestHeaders		✓
excludeRequestHeaders		✓
thirdPartyForCookies	✓	✓	✓	✓
Request stages during which actions can be executed.
Event	onBeforeRequest	onBeforeSendHeaders	onHeadersReceived	onAuthRequired
AddRequestCookie		✓
AddResponseCookie			✓
AddResponseHeader			✓
CancelRequest	✓	✓	✓	✓
EditRequestCookie		✓
EditResponseCookie			✓
IgnoreRules	✓	✓	✓	✓
RedirectByRegEx	✓		✓
RedirectRequest	✓		✓
RedirectToEmptyDocument	✓		✓
RedirectToTransparentImage	✓		✓
RemoveRequestCookie		✓
RemoveRequestHeader		✓
RemoveResponseCookie			✓
RemoveResponseHeader			✓
SendMessageToExtension	✓	✓	✓	✓
SetRequestHeader		✓

Note: Applicable stages can be further constrained by using the "stages" attribute.

Note: Redirects initiated by a redirect action use the original request method for the redirect, with one exception: If the redirect is initiated at the onHeadersReceived stage, then the redirect will be issued using the GET method.

Example: It is possible to combine a new chrome.declarativeWebRequest.RequestMatcher({contentType: ["image/jpeg"]}) condition with a new chrome.declarativeWebRequest.CancelRequest() action because both of them can be evaluated in the onHeadersReceived stage. It is, however, impossible to combine the request matcher with a new chrome.declarativeWebRequest.SetRequestHeader() because request headers cannot be set any more by the time the content type has been terminated.

Using priorities to override rules #

Rules can be associated with priorities as described in the Events API. This mechanism can be used to express exceptions. The following example will block all requests to images named "evil.jpg" except on the server "myserver.com".

var rule1 = {
  priority: 100,
  conditions: [
    new chrome.declarativeWebRequest.RequestMatcher({
        url: { pathEquals: 'evil.jpg' } })
  ],
  actions: [
    new chrome.declarativeWebRequest.CancelRequest()
  ]
};
var rule2 = {
  priority: 1000,
  conditions: [
    new chrome.declarativeWebRequest.RequestMatcher({
      url: { hostSuffix: '.myserver.com' } })
  ],
  actions: [
    new chrome.declarativeWebRequest.IgnoreRules({
      lowerPriorityThan: 1000 })
  ]
};
chrome.declarativeWebRequest.onRequest.addRules([rule1, rule2]);

It is important to recognize that the IgnoreRules action is not persisted across request stages. All conditions of all rules are evaluated at each stage of a web request. If an IgnoreRules action is executed, it applies only to other actions that are executed for the same web request in the same stage.

Summary

Types

AddRequestCookie

Adds a cookie to the request or overrides a cookie, in case another cookie of the same name exists already. Note that it is preferred to use the Cookies API because this is computationally less expensive.

Properties

cookie
RequestCookie
Cookie to be added to the request. No field may be undefined.

AddResponseCookie

Adds a cookie to the response or overrides a cookie, in case another cookie of the same name exists already. Note that it is preferred to use the Cookies API because this is computationally less expensive.

Properties

cookie
ResponseCookie
Cookie to be added to the response. The name and value need to be specified.

AddResponseHeader

Adds the response header to the response of this web request. As multiple response headers may share the same name, you need to first remove and then add a new response header in order to replace one.

Properties

name
string
HTTP response header name.
value
string
HTTP response header value.

CancelRequest

Declarative event action that cancels a network request.

EditRequestCookie

Edits one or more cookies of request. Note that it is preferred to use the Cookies API because this is computationally less expensive.

Properties

filter
RequestCookie
Filter for cookies that will be modified. All empty entries are ignored.
modification
RequestCookie
Attributes that shall be overridden in cookies that machted the filter. Attributes that are set to an empty string are removed.

EditResponseCookie

Edits one or more cookies of response. Note that it is preferred to use the Cookies API because this is computationally less expensive.

Properties

filter
FilterResponseCookie
Filter for cookies that will be modified. All empty entries are ignored.
modification
ResponseCookie
Attributes that shall be overridden in cookies that machted the filter. Attributes that are set to an empty string are removed.

FilterResponseCookie

A filter of a cookie in HTTP Responses.

Properties

ageLowerBound
number optional
Inclusive lower bound on the cookie lifetime (specified in seconds after current time). Only cookies whose expiration date-time is set to 'now + ageLowerBound' or later fulfill this criterion. Session cookies do not meet the criterion of this filter. The cookie lifetime is calculated from either 'max-age' or 'expires' cookie attributes. If both are specified, 'max-age' is used to calculate the cookie lifetime.
ageUpperBound
number optional
Inclusive upper bound on the cookie lifetime (specified in seconds after current time). Only cookies whose expiration date-time is in the interval [now, now + ageUpperBound] fulfill this criterion. Session cookies and cookies whose expiration date-time is in the past do not meet the criterion of this filter. The cookie lifetime is calculated from either 'max-age' or 'expires' cookie attributes. If both are specified, 'max-age' is used to calculate the cookie lifetime.
domain
string optional
Value of the Domain cookie attribute.
expires
string optional
Value of the Expires cookie attribute.
httpOnly
string optional
Existence of the HttpOnly cookie attribute.
maxAge
number optional
Value of the Max-Age cookie attribute
name
string optional
Name of a cookie.
path
string optional
Value of the Path cookie attribute.
secure
string optional
Existence of the Secure cookie attribute.
sessionCookie
boolean optional
Filters session cookies. Session cookies have no lifetime specified in any of 'max-age' or 'expires' attributes.
value
string optional
Value of a cookie, may be padded in double-quotes.

HeaderFilter

Filters request headers for various criteria. Multiple criteria are evaluated as a conjunction.

Properties

nameContains
string[] | string optional
Matches if the header name contains all of the specified strings.
nameEquals
string optional
Matches if the header name is equal to the specified string.
namePrefix
string optional
Matches if the header name starts with the specified string.
nameSuffix
string optional
Matches if the header name ends with the specified string.
valueContains
string[] | string optional
Matches if the header value contains all of the specified strings.
valueEquals
string optional
Matches if the header value is equal to the specified string.
valuePrefix
string optional
Matches if the header value starts with the specified string.
valueSuffix
string optional
Matches if the header value ends with the specified string.

IgnoreRules

Masks all rules that match the specified criteria.

Properties

hasTag
string optional
If set, rules with the specified tag are ignored. This ignoring is not persisted, it affects only rules and their actions of the same network request stage. Note that rules are executed in descending order of their priorities. This action affects rules of lower priority than the current rule. Rules with the same priority may or may not be ignored.
lowerPriorityThan
number optional
If set, rules with a lower priority than the specified value are ignored. This boundary is not persisted, it affects only rules and their actions of the same network request stage.

RedirectByRegEx

Redirects a request by applying a regular expression on the URL. The regular expressions use the RE2 syntax.

Properties

from
string
A match pattern that may contain capture groups. Capture groups are referenced in the Perl syntax ($1, $2, ...) instead of the RE2 syntax (\1, \2, ...) in order to be closer to JavaScript Regular Expressions.
to
string
Destination pattern.

RedirectRequest

Declarative event action that redirects a network request.

Properties

redirectUrl
string
Destination to where the request is redirected.

RedirectToEmptyDocument

Declarative event action that redirects a network request to an empty document.

RedirectToTransparentImage

Declarative event action that redirects a network request to a transparent image.

RemoveRequestCookie

Removes one or more cookies of request. Note that it is preferred to use the Cookies API because this is computationally less expensive.

Properties

filter
RequestCookie
Filter for cookies that will be removed. All empty entries are ignored.

RemoveRequestHeader

Removes the request header of the specified name. Do not use SetRequestHeader and RemoveRequestHeader with the same header name on the same request. Each request header name occurs only once in each request.

Properties

name
string
HTTP request header name (case-insensitive).

RemoveResponseCookie

Removes one or more cookies of response. Note that it is preferred to use the Cookies API because this is computationally less expensive.

Properties

filter
FilterResponseCookie
Filter for cookies that will be removed. All empty entries are ignored.

RemoveResponseHeader

Removes all response headers of the specified names and values.

Properties

name
string
HTTP request header name (case-insensitive).
value
string optional
HTTP request header value (case-insensitive).

RequestCookie

A filter or specification of a cookie in HTTP Requests.

Properties

name
string optional
Name of a cookie.
value
string optional
Value of a cookie, may be padded in double-quotes.

RequestMatcher

Matches network events by various criteria.

Properties

contentType
string[] optional
Matches if the MIME media type of a response (from the HTTP Content-Type header) is contained in the list.
excludeContentType
string[] optional
Matches if the MIME media type of a response (from the HTTP Content-Type header) is not contained in the list.
excludeRequestHeaders
HeaderFilter[] optional
Matches if none of the request headers is matched by any of the HeaderFilters.
excludeResponseHeaders
HeaderFilter[] optional
Matches if none of the response headers is matched by any of the HeaderFilters.
firstPartyForCookiesUrl
events.UrlFilter optional
Deprecated. Ignored since release 82.
Matches if the conditions of the UrlFilter are fulfilled for the 'first party' URL of the request. The 'first party' URL of a request, when present, can be different from the request's target URL, and describes what is considered 'first party' for the sake of third-party checks for cookies.
requestHeaders
HeaderFilter[] optional
Matches if some of the request headers is matched by one of the HeaderFilters.
resourceType
webRequest.ResourceType[] optional
Matches if the request type of a request is contained in the list. Requests that cannot match any of the types will be filtered out.
responseHeaders
HeaderFilter[] optional
Matches if some of the response headers is matched by one of the HeaderFilters.
stages
Stage[] optional
Contains a list of strings describing stages. Allowed values are 'onBeforeRequest', 'onBeforeSendHeaders', 'onHeadersReceived', 'onAuthRequired'. If this attribute is present, then it limits the applicable stages to those listed. Note that the whole condition is only applicable in stages compatible with all attributes.
thirdPartyForCookies
boolean optional
Deprecated. Ignored since release 87.
If set to true, matches requests that are subject to third-party cookie policies. If set to false, matches all other requests.
url
events.UrlFilter optional
Matches if the conditions of the UrlFilter are fulfilled for the URL of the request.

ResponseCookie

A specification of a cookie in HTTP Responses.

Properties

domain
string optional
Value of the Domain cookie attribute.
expires
string optional
Value of the Expires cookie attribute.
httpOnly
string optional
Existence of the HttpOnly cookie attribute.
maxAge
number optional
Value of the Max-Age cookie attribute
name
string optional
Name of a cookie.
path
string optional
Value of the Path cookie attribute.
secure
string optional
Existence of the Secure cookie attribute.
value
string optional
Value of a cookie, may be padded in double-quotes.

SendMessageToExtension

Triggers the onMessage event.

Properties

message
string
The value that will be passed in the message attribute of the dictionary that is passed to the event handler.

SetRequestHeader

Sets the request header of the specified name to the specified value. If a header with the specified name did not exist before, a new one is created. Header name comparison is always case-insensitive. Each request header name occurs only once in each request.

Properties

name
string
HTTP request header name.
value
string
HTTP request header value.

Stage

Enum

"onBeforeRequest", "onBeforeSendHeaders", "onHeadersReceived", or "onAuthRequired"

Events

onMessage

chrome.declarativeWebRequest.onMessage.addListener(listener: function)

Fired when a message is sent via SendMessageToExtension from an action of the declarative web request API.

Event

listener
function
The listener parameter should be a function that looks like this:
(details: object) => {...}
- details
  object
  frameId
  number
  The value 0 indicates that the request happens in the main frame; a positive value indicates the ID of a subframe in which the request happens. If the document of a (sub-)frame is loaded (type is main_frame or sub_frame), frameId indicates the ID of this frame, not the ID of the outer frame. Frame IDs are unique within a tab.
  message
  string
  The message sent by the calling script.
  method
  string
  Standard HTTP method.
  parentFrameId
  number
  ID of frame that wraps the frame which sent the request. Set to -1 if no parent frame exists.
  requestId
  string
  The ID of the request. Request IDs are unique within a browser session. As a result, they could be used to relate different events of the same request.
  stage
  Stage
  The stage of the network request during which the event was triggered.
  tabId
  number
  The ID of the tab in which the request takes place. Set to -1 if the request isn't related to a tab.
  timeStamp
  number
  The time when this signal is triggered, in milliseconds since the epoch.
  type
  webRequest.ResourceType
  How the requested resource will be used.
  url
  string

onRequest

chrome.declarativeWebRequest.onRequest.addListener(listener: function)

Event

listener
function
The listener parameter should be a function that looks like this:
() => {...}