zer0

A browser for people who live inside one. Vertical tabs, containers that are genuinely separate, one bar that does everything, nothing permanent between you and the page. WebKit engine, Rust core, native Swift shell, MIT.

Why

The browser is where a person's working day happens — and open source keeps treating that surface as something to get to later, on the theory that the engine is the hard part and the chrome can be a settings dialog with eleven tabs. zer0 does not take that trade: here, the interface is the product.

It started with firefox-airtraffic, an extension built because one specific thing was missing — and solving that one thing left the rest of the list exactly where it was. zer0 is the rest of the list. The full argument, decision by decision with what each one cost, is in Taste is not a method.

Settings	Extension consent

What it does

• Spaces — each space owns its cookie jar: two logins to the same site at once. An ephemeral space writes nothing to disk, ever.
• Air traffic — rules that send each URL to the space it belongs to.
• Tabs — favorites follow you everywhere, pins stay put, today's tabs archive themselves after twelve untouched hours.
• Split view — ⌘\ pairs two tabs side by side; ⇧⌘\ moves the keyboard.
• One bar — ⌘T and ⌘L are the same input for navigating, searching and switching tabs. The ranking lives in the core.
• Nothing on the page — no title bar, no toolbar: 38–90pt given back on every window, forever.
• The keymap you already have — Chrome-compatible, one binding per shortcut, stored are only your changes.
• Downloads that do not lie — no invented progress bars, no silent overwrites, honest names for interrupted files.
• Site icons without the tell — fetched anonymously, cached per space.
• Chrome extensions — paste a store link; every permission explained in plain language before anything runs, worst first.
• An assistant — ⌘E opens a conversation about the page you are on. Bring your own key (Anthropic, OpenAI, Gemini, or local Ollama); no tool runs until somebody approves that exact tool.

Build and run

Rust and Xcode, macOS 15.4 or newer.

./scripts/build.sh              # debug build → apple/.build/Zer0.app
./scripts/build.sh release      # optimised
open apple/.build/Zer0.app

./scripts/check.sh is the gate — fmt, clippy, the Rust suite, the decision record, the Swift suite. Green is the definition of done.

Where this is

Development. You can build it and run it; there is nothing to download. The bundle is ad-hoc signed (runs on the machine that built it, Gatekeeper refuses a copy), no notarisation, no release yet. Not every Chrome extension will work — chrome.debugger in particular is declined by policy, not missed by the engine.

Going deeper

docs/adr/	One file per decision — why the code is this way, what it cost, and the test that goes red if it is undone. Start here.
DESIGN.md	The design system: every token, with the criterion for reaching for it.
CONTRIBUTING.md	Build steps, generated bindings, and how a decision gets recorded.
docs/webkit.md	Running against a newer WebKit, embedding one, and the signing consequences.
docs/licensing.md	The dependency audit and the LGPL compliance checklist. Read before a release, not after.
Roadmap	What is intended, not what is done: the pinned epics — first release, Linux, core debt — and the epic label for the rest.
SECURITY.md	How to report a vulnerability: in private, never as a public issue.

Licence

MIT for the code in this repository — see LICENSE. WebKit is LGPL-2.1-or-later; a build that embeds it inherits obligations MIT does not describe, mapped in docs/licensing.md.