This event is fired just before sending headers. If your extension or some other extension modified headers in onBeforeSendHeaders, you'll see the modified version here.

This event is informational only.


  listener,             // function
  filter,               //  object
  extraInfoSpec         //  optional array of strings

Events have three functions:

addListener(callback, filter, extraInfoSpec)
Adds a listener to this event.
Stop listening to this event. The listener argument is the listener to remove.
Check whether listener is registered for this event. Returns true if it is listening, false otherwise.

addListener syntax



Function that will be called when this event occurs. The function will be passed the following arguments:

object. Details about the request. See details below.
webRequest.RequestFilter. A filter that restricts the events that will be sent to this listener.
array of string. Extra options for the event. You can only pass one value here:
  • "requestHeaders": include the request headers in the details object passed to the listener

Additional objects


string. URL of the document in which the resource will be loaded. For example, if the web page at "https://example.com" contains an image or an iframe, then the documentUrl for the image or iframe will be "https://example.com". For a top-level document, documentUrl is undefined.
integer. Zero if the request happens in the main frame; a positive value is 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.
string. Standard HTTP method: for example, "GET" or "POST".

string. URL of the resource which triggered the request. For example, if "https://example.com" contains a link, and the user clicks the link, then the originUrl for the resulting request is "https://example.com".

The originUrl is often but not always the same as the documentUrl. For example, if a page contains an iframe, and the iframe contains a link that loads a new document into the iframe, then the documentUrl for the resulting request will be the iframe's parent document, but the originUrl will be the URL of the document in the iframe that contained the link.

integer. ID of the frame that contains the frame which sent the request. Set to -1 if no parent frame exists.

object. This property is present only if the request is being proxied. It contains the following properties:

string. The hostname of the proxy server.
integer. The port number of the proxy server.

string. The type of proxy server. One of:

  • "http": HTTP proxy (or SSL CONNECT for HTTPS)
  • "https": HTTP proxying over TLS connection to proxy
  • "socks": SOCKS v5 proxy
  • "socks4": SOCKS v4 proxy
  • "direct": no proxy
  • "unknown": unknown proxy
string. Username for the proxy service.
boolean. True if the proxy will perform domain name resolution based on the hostname supplied, meaning that the client should not do its own DNS lookup.
integer. Failover timeout in seconds. If the proxy connection fails, the proxy will not be used again for this period.
string. The ID of the request. Request IDs are unique within a browser session, so you can use them to relate different events associated with the same request.
webRequest.HttpHeaders. The HTTP request headers that have been sent out with this request.
integer. ID of the tab in which the request takes place. Set to -1 if the request isn't related to a tab.
number. The time when this event fired, in milliseconds since the epoch.
webRequest.ResourceType. The type of resource being requested: for example, "image", "script", "stylesheet".
string. Target of the request.

Browser compatibility

ChromeEdgeFirefoxFirefox for AndroidOpera
Basic support Yes144548 Yes
details.frameId Yes144548 Yes
details.method Yes144548 Yes
details.originUrl No No4848 No
details.parentFrameId Yes144548 Yes
details.proxyInfo No No5757 No
details.requestId Yes144548 Yes
details.requestHeaders Yes144548 Yes
details.tabId Yes144548 Yes
details.timeStamp Yes144548 Yes
details.type Yes144548 Yes
details.url Yes144548 Yes


This code logs all cookies that will be sent in making requests to the target match pattern:

// The target match pattern
var targetPage = "*://*.google.ca/*";

// Log cookies sent with this request
function logCookies(e) {
  for (var header of e.requestHeaders) {
    if (header.name == "Cookie") {

// Listen for onSendHeaders, and pass
// "requestHeaders" so we get the headers
  {urls: [targetPage]},


This API is based on Chromium's chrome.webRequest API. This documentation is derived from web_request.json in the Chromium code.

Microsoft Edge compatibility data is supplied by Microsoft Corporation and is included here under the Creative Commons Attribution 3.0 United States License.

Document Tags and Contributors

Contributors to this page: wbamberg, andrewtruongmoz, Makyen
Last updated by: wbamberg,