1.2.4 • Public • Published

eyeo's WebExtension Ad-Filtering Solution

Contributor Covenant

This is a library that provides integration of eyeo's Ad Blocking Core for Chromium and Firefox extensions (like Adblock Plus). The Ad Blocking Core is in the core directory. See the content of that directory for further information.

Code of Conduct

All contributors to this project are required to read, and follow, our code of conduct.

Getting started

The library comes in two parts, ewe-api.js to be included in the extension's background page, and ewe-content.js to be loaded as a content script. Please download the latest build (or build the library yourself).

With two versions of the API, Manifest V2 and Manifest V3, there are two different manifest that are needed depending on which API you target.

Supported browsers

The webext-ad-filtering-solution (as a short term we use 'engine') is tested on the following versions:

Manifest V2:

  • Chromium 77 and 118
  • Firefox 68 and 119
  • Edge 79

Manifest V3:

  • Chromium 111 and 118
  • Edge 118

Manifest for V2

For Manifest V2, the extension's manifest.json is required to include the following configuration:

  "manifest_version": 2,
  "background": {
    "scripts": [
  "content_scripts": [
      "all_frames": true,
      "js": [
      "match_about_blank": true,
      "matches": [
      "run_at": "document_start"
  "permissions": [

Manifest for V3

For Manifest V3, the extension's manifest.json is required to include the following configuration:

  "manifest_version": 3,
  "background": {
    "service_worker": "background.js"
  "content_scripts": [
      "all_frames": true,
      "js": [
      "match_about_blank": true,
      "matches": [
      "run_at": "document_start"
  "permissions": [
  "host_permissions": [
  "declarative_net_request": <output from "subs-generate" script>

The example above requires a couple of changes and can't be used as-is.

The service_worker value needs be set to your built file for the background script, that includes ewe-api.js.

Please note that for the sample above, you need to make sure to set the value of declarative_net_request properly, as shown in the decalrativeNetRequest documentation. This mean you also need to add to your extension build the files that contains the rulesets declared in this section, as well as the text filter lists. Refer to the Manifest V3 documentation for more details.

The permission declarativeNetRequestWithHostAccess requires the host_permissions to be <all_urls>. You could use the declarativeNetRequest permission without setting host_permissions. But it would have the effect of preventing the filtering of content and limiting the blocking to network requests to those specified in host_permissions. The default configuration provided offers the most functionality.

Required permissions and why we need them

We require several permissions for the WebExt Ad-Filtering Solution to function correctly. The manifest file templates above include the required permissions. Here is why we need each one:

  • webNavigation: Gives access to the Web Navigation API, which we use to apply document-level allowing filters and to block popups.
  • webRequest: Gives access to the Web Request API. Used to apply URL filters in MV2, and to report on URL filters in MV3. Also used to retrieve sitekeys for a site.
  • webRequestBlocking (MV2 only): Allows blocking request based on URL filters in MV2.
  • declarativeNetRequest (MV3 only): Gives access to the Declarative Net Request API, which we use to apply URL filters in MV3.
  • storage: Gives access to storage APIs, which we use to store downloaded subscriptions, user's custom filters, etc.
  • unlimitedStorage: By default, extensions are only allowed 5MB of storage, which isn't enough for larger subscriptions. This permission removes that limit.
  • tabs: Gives access to some tab metadata, including the tab's URL, which is used to apply document-level allowing filters to the tab.
  • scripting (MV3 only): Used to apply content filters, including element hiding filters and snippet filters.
  • <all_urls>: Allows the WebExt Ad-Filtering Solution to act on all websites. Note that in MV2 manifests this goes in the permissions, but in MV3 manifests this goes in the new host_permissions section.

You can read more about browser extension permissions and their effects in Google's docs for MV2 permissions and MV3 permissions


The API will be available in your own background scripts through the global EWE object. Please call EWE.start() to start blocking ads.

Note that in MV3 extensions, EWE.start() must be called in the first turn of the event loop so that it can attach event listeners.

Module bundlers (optional)

ewe-api.js is built as a UMD module (Universal Module Definition), and so it can also be used with module bundlers.

If using a module bundler do not add ewe-api.js to your manifest.json. Consequently, there won't be a global EWE object.


const EWE = require("@eyeo/webext-ad-filtering-solution");


import * as EWE from "@eyeo/webext-ad-filtering-solution";

Snippet filters support

In order to enable support for snippet filters you have to get the snippets library separately and make it available to EWE:

import isolatedCode from "mv3.isolated.mjs";
import injectedCode from "mv3.injected.mjs";
EWE.snippets.setLibrary({isolatedCode, injectedCode});

Note mv3... artifacts are required to be used for both MV2 and MV3.

The integration of the machine learning models is expected to be done by clients of the snippet library.

Shared resources

There are some shared resources that are used by both webext-ad-filtering-solution & production code:

  • browser
    • Global is set by webextension-polyfill version 0.8.0.
  • browser.runtime.connect()/browser.runtime.onConnect
    • Channel name is prefixed with "ewe:".
  • browser.runtime.sendMessage()/browser.runtime.onMessage
    • Our messages are objects with a "type" property whose value is prefixed with "ewe:".
  • indexedDB.open()
    • Database name is prefixed with "EWE".
  • Web page links
  • browser.storage.local and browser.storage.session
    • Storage keys are prefixed with either "ewe:" or "abp:pref:".

During initialization the engine migrates legacy data from local storage to indexedDB. Files migrated have to be prefixed: file:. Files prefixed with file:/// will be ignored.

Notifications support

Using the notifications module is optional. To start using it, an initialisation is required:


One Click Allowlisting support

To enable One Click Allowlisting, you need to set the list of authorized public keys that can be used to authenticate allowlisting requests.


See the allowlisting module docs for more detail.

New keypairs can be created with the correct algorithm and settings by using our keypair creation script.

npm run create-allowlisting-keypair

See the Development section below for details on running our scripts and other EWE development tasks. Keys can also be generated using other programs like OpenSSL. The keys use the RSASSA-PKCS1-v1_5 algorithm, SHA512 hash and 4096 bit long modulus. Additionally, when passed to setAuthorizedKeys, the keys should be base64 encoded strings, in SPKI format.


For more information, please refer to the API documention.



  • Node >= 18
  • npm >= 9

Installing/Updating dependencies

npm install

Building the library

npm run build

Running Locally (and watch for changes)

npx webpack --watch

Custom builds

Our build script is a CLI program with a few additional flags that can be passed to it. It can list the options available if you ask for --help.

npm run build -- --help

There are some specific flags which might be useful to customise the build:

# Build only engine, no test extensions
npm run build -- --config-name engine

# Don't generate any sourcemaps
npm run build -- --no-devtool

In the background, this script is using Webpack. You can also see the webpack command line options for further information on these flags.

Managing Bundled Subscriptions in the test build

In MV3 extensions (and the MV3 test extension), subscriptions are bundled statically at build time. The bundled subscriptions are based on the custom subscriptions file. Bundled subscription are updated by the build script if this file changes.

One case to look out for when working with bundled subscriptions in tests is that subscriptions are NOT re-fetched if their filters have changed. If you need to re-fetch new filters and the list of subscriptions hasn't changed, you can use the --force-subscription-update flag to the build script.

npm run build -- --force-subscription-update
Using your own test-server instance

By default, the build script will start up the test server for updating bundled subscriptions. If you prefer to use a test server which is already running, you can use the --use-external-server flag.

npm run test-server&
npm run build -- --use-external-server

Release builds

By default, debug builds are created. If building the library to be used in another project you would want to create a release build.

npm run build -- --env release

Building the documentation

npm run docs

Linting the code

npm run lint


The library provides the listeners to observe the events:

  • EWE.allowlisting.onUnauthorized: Emitted when an allowlisting request is rejected
  • EWE.filters:
    • onAdded: Emitted when a new filter is added
    • onChanged: Emitted when a filter is either enabled or disabled or metadata changed
    • onRemoved: Emitted when a filter is removed
  • EWE.subscriptions:
    • onAdded: Emitted when a new subscription is added
    • onChanged: Emitted when any property of the subscription has changed
    • onRemoved: Emitted when a subscription is removed
  • EWE.debugging.onLogEvent: Emitted when having debug output
  • EWE.reporting.onBlockableItem: Emitted when any blockable item is matched

Use addListener(...) to subscribe and removeListener(...) to unsubscribe.

Manifest V3

See the Manifest V3 documentation for further explanations.


For full documentation about testing please refer to our testing document.


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