browserenginekit

What the source does

• FilesystemNone observedNo reads or writes in the source
• NetworkNone observedNo outbound calls in the source
• ShellNone observedNo commands run in the source
• DependenciesPinnedNothing floats
• SecretsNone foundNo keys in source

Five audit layers

Gates applied: no behavioural pass.

Audit 0.4.1 · source sha 8c7069c512a0 · 31 Oct 2026Report an issue or request a re-scan

• Publisherdpearson2699 GitHub userOwner of the repository this skill is read from
• Source folderdpearson2699/swift-ios-skills/skills/browserenginekitThe exact folder we audited
• LicenceNOASSERTIONAs the repository states it
• Commit pinned for this verdict8c7069c512a0A new audit runs when the source changes
• Repository statusNot archivedLast push 91 days ago
• Sandboxed runNot runSkills are read, not executed; layer L4 is skipped

Its 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…

---
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+:

```swift
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

Excerpt, first 6,000 characters of SKILL.md, verbatim from the audited commit. It is text from someone else’s repository, quoted so you can judge it before your agent reads it.

git clone https://github.com/dpearson2699/swift-ios-skills
git -C swift-ios-skills checkout 8c7069c512a0

Works in

1. 2026-10-31
   ✓SAFE B 89 / 100

   first audit · source 8c7069c512a0

Questions about browserenginekit

• github.com/dpearson2699/swift-ios-skills/tree/main/skills/browse — the audited source at commit 8c7069c512a0 and every finding aboveObserved · 31 Oct 2026

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