Open the same tab in two browser windows. In Chrome or Safari, you get two unconnected pages. In Arc, one window shows a placeholder. In Zen, it silently creates a duplicate.

In Refrax, the browser I built, both windows show the same page updating live. The same web page, in as many windows as you want.

This shouldn't be possible. WebKit's WKWebView can exist in exactly one view hierarchy at a time. With macOS 26, Apple added a SwiftUI API separating WebView from WebPage, so you can end up with multiple views referencing the same page. But if you try it, your app crashes. WebKit source code has a precondition with this comment: "We can't have multiple owning pages regardless, but we'll want to decide if it's an error, if we can handle it gracefully, and how deterministic it might even be..."

So here's how I did it.

CAPortalLayer is an undocumented private class that's been in macOS since 10.12. It mirrors a layer's composited output by referencing the same GPU memory, not copying it. Every scroll, animation, or repaint reflects instantly. This is what powers Liquid Glass effects, the iOS text selection magnifier, and ghost images during drag and drop. Apple uses portals for effects. I use them to put the same web page in two windows.

Refrax keeps one real WKWebView per tab and displays a CAPortalLayer mirror everywhere else. When you click a different window, the coordinator moves the real view there and the old window gets a portal. You can't tell which is which.

This sounds simple in theory, but making this actually work seamlessly took quite a lot of effort. Each macOS window has its own rendering context, and the context ID updates asynchronously, so creating a portal immediately captures a stale ID and renders nothing. The portal creation needs to be delayed, but delaying creates a visual gap. I capture a GPU snapshot using a private CoreGraphics function and place it behind the portal as a fallback. Another hard part is that none of it is documented. Portals are very capricious and would crash the app if you use them incorrectly. I had to inspect the headers and then disassemble the binaries to explore exactly how it works in order to build something robust.

I never worked on a browser before this, I've only been a user. I started using Arc in 2022. I remember asking for an invite, learning the shortcuts, slowly getting used to it. I didn't like it at first as it had too much Google Chrome in it for my taste, and I'd been using Safari at the time. But it grew on me, and by the time it was essentially abandoned and sold to Atlassian, I couldn't go back to Safari anymore. I tried everything: Zen, SigmaOS, Helium. None felt right, and I didn't want another Chromium fork. WebKit ships with the OS, but all you get is the rendering engine. Tabs, history, bookmarks, passwords, extensions, everything else has to be made separately. And so, being a very reasonable person, I decided to make my own Arc replacement from scratch.

And I did. Refrax is built in Swift and Objective-C with no external dependencies. The app itself is less than 30 MB. I have 393 tabs open right now using 442 MB of RAM; 150 tabs in Safari was already over 1 GB. I've been using it daily for over a month, and so have some of my friends.

The portal mirror is just one feature. The same approach, finding what Apple built for themselves and using it to create something they didn't think about, runs through the entire browser. You can tint your glass windows with adjustable blend modes and transparency. The sidebar in compact mode samples the page and matches the colors. And it has support for Firefox and Chrome extensions.

The alpha is public. Download from the linked website, enter REFRAX-ALPHA-HACKERNEWS to activate. No account needed. Telemetry is crash reports and a daily active-user ping, nothing else. And if you find a bug – I built this alone, so I'll actually read your report.

The browser was made as an Arc replacement, and so has most of its features.

Features currently available in the alpha version include: Pinned tabs, tab groups, tab filtering, tab sorting, favorites (Arc model), spaces with optionally different profiles, custom download paths, and authentication via TouchID or password, RSVP reader, split-view for tabs (2, 3, or 4), and a side panel that has its own tabs, per-tab volume and audio control, link previews, custom routing rules for links, you can make all mailto: links open gmail, open all links to a domain in a specific browser, etc., automatically detects phone numbers, flight numbers, and similar info on right click and shows relevant actions, can also convert measurements, can download videos from most services with yt-dlp integration, can be controlled from Claude Code or similar, and has a DSL for the commands, blocks APIs like page visibility, disables copy-paste blocking, strips tracker parameters, shortcuts app integration, calendar integration (will remind of meetings), handoff support, auto-detects and marks tabs as unread when you receive a new message, auto-add custom search engines, can show the memory use of each tab, supports Chrome, Firefox extensions, can pin window to be always on top, make it transparent, or show on every space, windowed fullscreen, tab screenshots and video recording, quick drag and drop shelf

Why not open source it? Pretty sure no one will try seriously unless it’s open source.

And you won’t get the flex without showing off the source.

Growing it as a business seems pretty hard and you kind of have a catch-22: non-developer audience probably doesn’t care about it, developer audience won’t touch it unless it’s open source.

This is a really clever use of CAPortalLayer. Feels like you're essentially bypassing the “one WKWebView per hierarchy” constraint by turning the problem into a rendering problem instead of a state problem.

Curious how you handle input events across mirrored views — does only the “real” view receive interaction and others proxy it, or is there some trick there too?

Nice one! Looking forward to trying it out. Have had the same grievances about Arc being abandone. Dia? … nah

that's a pretty genius use of the "portals" primitive; I suppose its akin to Portals in React-ish.

Although I've never needed to open 2 tabs of the same site and wanted them share the state.