cwbrowser: A New Browser Engine Written in Zig

cwbrowser is a new, lightweight web browser and rendering engine written from scratch in the Zig systems language. Developed over two years of solo engineering, the engine replaces the traditional Chromium (Blink), WebKit, or Gecko engines with a custom implementation of the HTML parser, CSS cascade, layout engine, and paint pipeline.

Technical Architecture

cwbrowser utilizes a modern systems language to achieve high performance and a small footprint. The architecture is divided into the following components:

  • Rendering Engine (Zig): The entire pipeline—including the tokenizer, DOM construction, CSS parser, and layout/paint stages—is hand-written in Zig. This approach leverages manual memory management and avoids a garbage collector or hidden runtime to maximize efficiency.
  • JavaScript Engine (V8): To avoid the decade-scale effort of rebuilding a modern JIT-compiling VM, cwbrowser embeds Google's V8 engine. V8 is bound to the custom DOM, allowing the browser to handle JavaScript execution while maintaining a custom rendering path.
  • Layout and Paint: The engine implements a hand-written block/inline layout and a paint pipeline designed to render pixels to match the Acid3 reference.

Performance and Standards Conformance

According to the developer, cwbrowser achieves a perfect 100/100 score on the Acid3 test, which is a benchmark for standards conformance. In early benchmarking, the developer claims the engine is roughly 2× faster than Google Chrome on the same hardware.

Community Feedback and Technical Critiques

Following its announcement on Hacker News, the project received a mixed response from the technical community. While some praised the achievement of a solo developer, several experts raised critical points regarding the browser's current state and validity:

Standards and Testing

Critics pointed out that Acid3 is an outdated benchmark. One user noted that modern specifications have diverged from the test to the point where current versions of Chrome, Safari, and Firefox no longer pass it perfectly. Furthermore, the community emphasized that Acid3 is a minimal fraction of the total web platform requirements.

"Acid3 is 100 tests but to have a browser that works on any real percentage of the internet you need to pass the over 52,000 tests and nearly two million subtests that make up the Web Platform Tests."

Verification and Transparency

Several users expressed skepticism regarding the authenticity of the project, citing a lack of available source code, binaries, or detailed technical documentation. Some described the landing page as "vibe coded" or "AI slop," suggesting the project may be agentically generated rather than hand-written.

Feature Gaps

Technical observers noted that based on available renders, the engine does not yet support SVG, and there were requests for further evidence of its ability to render modern, complex web pages beyond the Acid3 test.

Availability

A public preview build for macOS on Apple Silicon is currently being prepared for release. The project is currently not open source, and interested users can sign up for beta notifications via email.

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