Architecture

OpenArch is a native Mac app around Chromium. The sidebar, the command bar and everything else you see around the page are Swift. The pages are Chrome.

Swift / AppKit / SwiftUI app        App/Sources/OpenArch
  sidebar, command bar, spaces, library, Arc import, AI features
        │  a narrow Objective-C API
OpenArchCore (Objective-C++)        App/Sources/OpenArchCore
  OACEngine, OACProfile, OACPane
        │
CEF (Chromium) with codecs          Vendor/cef

Every tab is a real Chrome tab

Each tab is an OACPane: a Chrome-style CEF browser in a borderless window of its own, attached as a child window over OpenArch’s content area. To Chromium it is an ordinary Chrome tab, so extensions, chrome.tabs, side panels, DevTools, the password manager and chrome:// pages work as in Chrome. Browsers embedded the simpler way (“Alloy” style) lack most of that; spikes/01-cef/RESULTS.md has the details.

CEF allows one Chrome-style browser per window. Split view therefore places several of these windows side by side.

Profiles

Every space uses a profile, an OACProfile, which is a Chromium profile with its own cookies, logins, history, passwords and extensions. A private window gets a profile that lives only in memory.

The extension built in

OpenArch loads a small extension of its own into every profile (App/Resources/BuiltinExtensions/openarch). It tells the sidebar which tabs play audio and video, and what, and which share the screen. It reports through the page’s console, which OpenArch reads.

The AI features

OpenArch does not talk to a model itself. It starts the Claude Code command line tool and reads its answers; see How OpenArch talks to Claude.

The sharing format, its cryptography and the relay client are a Swift package of their own (Shared/), used by the Mac and the iOS app. The relay is a Cloudflare Worker (relay/). docs/sharing.md describes the format and the threat model; How sharing works is the short version.

The repository

Folder	What is in it
`App/`	The Mac app
`iOS/`	OpenArch for iPhone and iPad
`Shared/`	The Swift package both use for sharing
`relay/`	The relay for live shares, a Cloudflare Worker
`website/`	openarch.app, and `website/s/`, which shows shared links to people without OpenArch
`docs-site/`	These docs
`docs/`	The sharing format and App Store notes
`scripts/`	Fetching, updating and building CEF; drawing the icons
`spikes/`	The first experiments with CEF