Creating Safari Web Inspector extensions

At a glance

Project structure

Source bundle/
├── Open Graph/
│   ├── macOS (App)/
│   │   ├── AppDelegate.swift
│   │   ├── Base.lproj/
│   │   │   └── Main.storyboard
│   │   └── Open Graph.entitlements
│   ├── Shared (App)/
│   │   ├── ViewController.swift
│   │   └── Resources/
│   │       └── Script.js
│   ├── Shared (Extension)/
│   │   ├── SafariWebExtensionHandler.swift
│   │   └── Resources/
│   │       ├── devtools_background.js
│   │       └── devtools_tab.js
│   ├── Open Graph.xcodeproj/
│   │   ├── .xcodesamplecode.plist
│   │   └── project.pbxproj
│   └── macOS (Extension)/
│       └── Info.plist
└── Configuration/
    └── SampleCode.xcconfig

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: JavaScript, Swift.
• The verified tree contains 7 project/configuration file(s) and 3 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["ViewController"]
    N3["SafariWebExtensionHandler"]
    N4["SafariServices APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

Open Graph/macOS (App)/AppDelegate.swift:10 — architecture anchor

@main
class AppDelegate: NSObject, NSApplicationDelegate {

    func applicationDidFinishLaunching(_ notification: Notification) {

    }

    func applicationShouldTerminateAfterLastWindowClosed(_ sender: NSApplication) -> Bool {
        return true
    }

}

Interpretation

The arrows summarize the source-visible entry, role-named types or folders, and framework direction; when nodes come from structural folders, the sequence is a high-level interpretation rather than proof that every adjacent node calls the next. Ownership is claimed only where the next section cites a stored property or assignment. The diagram is intentionally limited to the dominant path into Safari Services.

Ownership and state

classDiagram
    ViewController o-- WKWebView : webView

Ownership evidence

Open Graph/Shared (App)/ViewController.swift:18 — stored dependency or nearest verified ownership anchor

class ViewController: PlatformViewController, WKNavigationDelegate, WKScriptMessageHandler {
    // ...
    @IBOutlet var webView: WKWebView!
    // ...
}

Composition arrows indicate a source-visible construction expression or locally owned value state; aggregation means the owner stores or receives a dependency without proving exclusive lifetime ownership.

Concurrency, scheduling, and thread safety

Evidence limit: actor isolation, async/await, or Task creation does not by itself prove background-thread execution; Sendable conformance alone does not prove thread-safe mutation.

@MainActor/MainActor.run, DispatchQueue.main, and RunLoop.main are reported as distinct isolation, queue, and event-loop mechanisms. A plain Task is kept separate from Task.detached; neither is labeled as a background thread.

Reference code

Open Graph/Shared (App)/ViewController.swift:39 — representative execution boundary

            DispatchQueue.main.async {
                webView.evaluateJavaScript("show('mac', \(state.isEnabled))")
            }

State propagation, frameworks, and dependencies

Evidence limit: an import proves a source-level compilation dependency at the cited line; it does not prove runtime use, architectural adoption, or whether a Swift package is a direct application dependency.

receive(on:) describes downstream delivery scheduling, while subscribe(on:) describes upstream subscription/request/cancel scheduling. An import Combine alone establishes neither behavior nor a Store, reducer, Redux, or other application architecture.

Class and protocol design

Open Graph/macOS (App)/AppDelegate.swift:11 — representative type boundary

@main
class AppDelegate: NSObject, NSApplicationDelegate {
    // ...
        return true
    // ...
}

No local protocol conformance is claimed as protocol-oriented design; external framework conformances are listed only as dependencies.

Access control

Reference code

Open Graph/macOS (App)/AppDelegate.swift:11 — representative boundary

@main
class AppDelegate: NSObject, NSApplicationDelegate {
    // ...
        return true
    // ...
}

Swift declarations without a modifier are internal; explicit private, fileprivate, private(set), public, or open entries above are interpreted by language semantics. Objective-C/C samples instead rely on header and implementation boundaries, which are not equivalent to Swift lexical privacy.

Logic ownership and placement

Design patterns

Naming conventions

• Types: Controller: ViewController; Delegate: AppDelegate; Handler: SafariWebExtensionHandler.
• Protocols: no local protocol declaration in the scanned source.
• Methods: applicationDidFinishLaunching, applicationShouldTerminateAfterLastWindowClosed, viewDidLoad, webView, userContentController, beginRequest, show, openPreferences.
• Files: Open Graph/macOS (App)/AppDelegate.swift, Open Graph/Shared (App)/ViewController.swift, Open Graph/Shared (Extension)/SafariWebExtensionHandler.swift.

Architecture takeaways

• AppDelegate is the main source-visible entry or composition anchor for this sample.
• Framework work reaches Cocoa, SafariServices, WebKit through a deliberately small high-level chain; the detailed API graph remains inside the cited implementation files.
• Stored-property evidence identifies lifecycle collaboration; it does not by itself prove exclusive object ownership.
• Access-control conclusions separate verified language visibility from the likely design rationale.
• The source does not justify labeling the design protocol-oriented.

Source map

• Official Apple documentation