/browserenginekit

name: browserenginekit
description: "Build alternative browser engines using BrowserEngineKit. Use when developing a non-WebKit browser engine for iOS/iPadOS in supported regions, managing web content/rendering/networking extension processes, configuring GPU and networking process capabilities, checking alternative-engine device eligibility, or reviewing BrowserEngineKit entitlements and Info.plist setup."

BrowserEngineKit

Framework for building web browsers with alternative (non-WebKit) rendering engines on iOS and iPadOS. Provides process isolation, XPC communication, capability management, and system integration for browser apps that implement their own HTML/CSS/JavaScript engine. Examples target Swift 6.3 and current Apple SDKs.

BrowserEngineKit is a specialized framework. Alternative browser engines are available only through Apple-approved entitlement profiles and supported-region device eligibility. EU support applies to eligible users on iOS 17.4+ and iPadOS 18+; Japan support starts with iOS 26.2 and adds explicit PAC/MIE security requirements for browser apps. Development and testing can occur anywhere. The companion frameworks BrowserEngineCore (low-level primitives) and BrowserKit (eligibility checks, data transfer) support the overall workflow.

Contents

• [Overview and Eligibility](#overview-and-eligibility)
• [Entitlements](#entitlements)
• [Architecture](#architecture)
• [Process Management](#process-management)
• [Extension Types](#extension-types)
• [Capabilities](#capabilities)
• [Layer Hosting and View Coordination](#layer-hosting-and-view-coordination)
• [Text Interaction](#text-interaction)
• [Sandbox and Security](#sandbox-and-security)
• [Downloads](#downloads)
• [Common Mistakes](#common-mistakes)
• [Review Checklist](#review-checklist)
• [References](#references)

Overview and Eligibility

Eligibility Checking

Use `BEAvailability` from the BrowserKit framework to check whether the device is eligible for alternative browser engines. `BEAvailability` is available on iOS/iPadOS 18.4+:

import BrowserKit

do {
    let eligible = try await BEAvailability.isEligible(for: .webBrowser)
    guard eligible else { return /* fall back or explain */ }
    // Device supports alternative browser engines
} catch {
    // Handle eligibility lookup failure
}

Eligibility depends on the device region and OS version. Do not hard-code region checks; rely on the system API.

Availability anchors: process APIs are iOS/iPadOS 17.4+, `BEDownloadMonitor` is iOS 18.2+, `.revision2` restricted sandbox is iOS 26+, and `RenderingExtensionFeature.coreML` is iOS 26.2+.

Entitlements

Browser App (Host)

The host app requires two entitlements:

| Entitlement | Purpose | |---|---| | `com.apple.developer.web-browser` | Enables default-browser candidacy | | `com.apple.developer.web-browser-engine.host` | Enables alternative engine extensions |

Both must be requested from Apple. The request process varies by region.

Extension Entitlements

Each extension target requires its type-specific entitlement set to `true`:

| Extension Type | Entitlement | |---|---| | Web content | `com.apple.developer.web-browser-engine.webcontent` | | Networking | `com.apple.developer.web-browser-engine.networking` | | Rendering | `com.apple.developer.web-browser-engine.rendering` |

Optional Entitlements

| Entitlement | Extension | Purpose | |---|---|---| | `com.apple.security.cs.allow-jit` | Web content | JIT compilation of scripts | | `com.apple.developer.kernel.extended-virtual-addressing` | Web content | Required alongside JIT | | `com.apple.developer.memory.transfer_send` | Rendering | Send memory attribution; value is host app bundle ID | | `com.apple.developer.memory.transfer_accept` | Web content | Accept memory attribution; value is host app bundle ID | | `com.apple.developer.web-browser-engine.restrict.notifyd` | Web content | Restrict notification daemon access |

Embedded Browser Engine (Non-Browser Apps)

Apps that are not browsers but embed an alternative engine for in-app browsing use different entitlements:

| Entitlement | Purpose | |---|---| | `com.apple.developer.embedded-web-browser-engine` | Enable embedded engine | | `com.apple.developer.embedded-web-browser-engine.engine-association` | Declare engine ownership |

`engine-association` is available starting iOS/iPadOS/Mac Catalyst 26.2 and is set to `first-party` when you own the engine or `third-party` when another developer owns it. Embedded engines use `arm64` only (not `arm64e`), cannot include browser extensions, and cannot use JIT compilation.

Japan-Specific Requirements

Browser apps distributed in Japan are supported on iOS 26.2+ and must adopt the current security mitigations Apple lists for Japan, including Pointer Authentication Codes and Memory Integrity Enforcement for relevant allocators and extension processes. Enable hardware memory tagging with `com.apple.security.hardened-process.checked-allocations`; Apple strongly recommends enabling it in the EU as well.

Architecture

A browser built with BrowserEngineKit consists of four components running in separate processes:

Host App (UI, coordination)
  |
  |-- XPC --> Web Content Extension (HTML parsing, JS, DOM)
  |-- XPC --> Networking Extension (URLSession, sockets)
  |-- XPC --> Rendering Extension (Metal, GPU, media)

The host app launches and manages all extensions. Extensions cannot launch other extensions. Extensions communicate with each other through anonymous XPC endpoints brokered by the host app.

Bootstrap Sequence

1. Host launches web content, networking, and rendering extensions 2. Host creates XPC connections to each extension 3. Host requests anonymous XPC endpoints from networking and rendering 4. Host sends both endpoints to the web content extension via a bootstrap message 5. Web content extension connects directly to networking and rendering

This architecture follows the principle of