Chrome MV3 Extensions
WebToApp runs Manifest V3 (and V2) Chrome extensions: content scripts, popups, options pages, a background context, and declarativeNetRequest rules. You can import a .crx/.zip, or install live from the Chrome Web Store via the Browser Extensions tab.
Supported manifest.json fields
| Field | Notes |
|---|---|
manifest_version | 2 or 3. |
name, version, description | Support __MSG_key__ i18n via _locales/<locale>/messages.json. |
default_locale | Base locale for i18n. |
content_scripts[] | matches, exclude_matches, js[], css[], run_at (document_start/end/idle, default idle), all_frames (default false), world ("MAIN" or default "ISOLATED"). Each entry becomes one internal module. |
action.default_popup / browser_action / page_action | Popup page. |
options_page / options_ui.page | Options page. |
background.service_worker / background.scripts[0] | Background context; background.type: "module" loads as an ES module. |
declarative_net_request.rule_resources[] | {id, enabled, path}. |
permissions, host_permissions, optional_permissions | Mapped to internal permission categories; unsupported ones produce a warning. |
chrome.* API support
A polyfill provides a broad chrome.* (and browser.*) surface. Core functional namespaces:
| Namespace | Functional highlights |
|---|---|
runtime | getURL, getManifest, sendMessage, onMessage, onInstalled, connect/onConnect, getPlatformInfo, id, lastError |
storage | local / sync / session + onChanged (sync maps to local; managed is a no-op) |
tabs | create, query, sendMessage, get, getCurrent, update + events |
scripting | executeScript, insertCSS, removeCSS, registerContentScripts, unregisterContentScripts, getRegisteredContentScripts |
cookies | Cookie access |
alarms | Scheduling |
declarativeNetRequest | Rule-based blocking/redirect (see below) |
downloads | download |
webRequest | onBeforeRequest can register real filtering via the native bridge |
i18n, notifications, permissions, contextMenus, commands | Supported |
Many other namespaces (windows, management, bookmarks, history, identity, system.*, offscreen, tts, …) are present as stubs returning defaults. See the API Reference for the per-API status.
No true world isolation
Android WebView has a single JavaScript context. world: "ISOLATED" and world: "MAIN" are both injected into the same window via evaluateJavascript; isolation is simulated by each extension overwriting globalThis.chrome and capturing its own extension id in a closure. Don't rely on real isolation between extensions.
Background is a hidden WebView
The MV3 "service worker" runs in a hidden WebView with a service-worker environment shim (self, clients, caches, install/activate/fetch events). In the background, fetch() is rewritten to go through a native HTTP path that bypasses CORS. It is not a real service worker.
declarativeNetRequest
Supported actions: block, allow, redirect, modifyHeaders, upgradeScheme, allowAllRequests. Conditions support urlFilter / regexFilter, resourceTypes, initiatorDomains, requestMethods, and more. Prefer DNR over webRequestBlocking (which is unsupported).
Resource URLs
chrome.runtime.getURL(path) returns https://localhost/__ext__/<EXT_ID>/<path>, intercepted by the resource interceptor and served from the extension's bundled files.
Unsupported permissions (warning only)
nativeMessaging, debugger, proxy, webRequestBlocking, management, devtools, bookmarks, identity, tabCapture, and similar produce a warning and are not functional.
Installing
- Import a
.crx(CRX2/CRX3 parsed directly) or.zip. - Chrome Web Store — the Browser Extensions tab searches the store live by keyword (or paste a store URL / extension ID) and installs on demand through the CRX pipeline. Live search requires a network that can reach Google.