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tech 1 August 2026

Show HN: A New Browser Passes Acid3 with Flying Colors

After two years of solo development, cwbrowser, a browser written in Zig, aces the Acid3 test with a perfect score of 100/100. Learn about the journey and innovations behind this ambitious project.

Article inspired by the original source
Show HN: I worked on a new browser for 2 years, today it passed Acid 3 ↗ code.intellios.ai

Introduction

In the world of web browsers, it is rare to see innovation that does not rely on existing rendering engines like Blink, WebKit, or Gecko. However, cwbrowser challenges this norm by being entirely built from scratch using the Zig programming language. After two years of intense work, this lightweight and fast browser has passed the Acid3 test, a major milestone in terms of web standards compliance.

What is cwbrowser?

cwbrowser is a desktop web browser based on a rendering engine fully developed in Zig. Zig is a programming language known for its manual memory management and lack of garbage collector, which allows for increased performance and memory efficiency. Unlike other browsers, cwbrowser does not use existing engines for HTML or CSS. Each component, from the tokenizer to the CSS cascade, is handcrafted.

Why Build a Browser from Scratch?

One might ask: why reinvent the wheel? The answer lies in the desire to create a rendering engine that is both comprehensible from end to end and capable of superior performance. By avoiding the inherited complexity of existing engines, cwbrowser offers a lightweight alternative that even surpasses Chrome in terms of speed on the same hardware, with approximately twice the performance in early tests.

The Acid3 Test

The Acid3 test is a standardized benchmark that evaluates a browser's compliance with modern web specifications. Achieving a score of 100/100 is a mark of quality and compatibility. This perfect score obtained by cwbrowser demonstrates its ability to compete with the big players while being built with a radically different approach.

The Structure of the Rendering Engine

HTML & DOM

cwbrowser's engine starts with a tokenizer and DOM tree builder developed from scratch. This allows smooth interaction between the engine and the DOM, while integrating Google's V8 JavaScript engine for script execution.

CSS

An original CSS parser and cascade handle selectors, specificity, and the box model, providing information to the layout pass.

Layout and Painting

The layout and painting pipeline are hand-written, ensuring pixel-perfect rendering that matches the Acid3 reference.

Performance and Efficiency

One of cwbrowser's primary goals is to provide a fast and efficient alternative to existing browsers. Thanks to its lightweight design, free of massive library dependencies, cwbrowser is capable of impressive performance, notably using Google V8 solely for JavaScript.

Conclusion

cwbrowser is more than just an experimental browser; it represents a new path in rendering engine development. By combining a lightweight architecture with rigorous standards compliance, it offers a fast and compliant user experience. Whether for curious developers or companies looking to explore new solutions, cwbrowser deserves attention.

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