A new project called Bez aims to create a web rendering engine by translating technical specifications and test suites into executable code. The initiative, reported by Hacker News, uses automated generation rather than manual development to build components of a browser engine.

The engine, written primarily in Rust, was developed by analyzing three major browsers — Chromium, Firefox, and WebKit — alongside the Web Platform Tests (WPT), a comprehensive collection of web standards tests. By comparing outputs across these browsers, the system identifies specifications that produce consistent rendering behavior. When discrepancies arise, the process iteratively refines candidate implementations until convergence is achieved.

Generated code is then committed as standard Rust modules, enabling integration into downstream projects. The approach allows for lightweight, modular engines tailored to specific use cases, such as embedding in applications or analyzing web content without requiring full browser capabilities.

Bez supports two build modes: a complete engine for general use, and a content-scoped variant that includes only the features actually used by a given site or application. This reduces memory usage and processing demands, improving performance on constrained devices.

Testing results show high agreement among the three reference browsers across the majority of test cases. Of 2.28 million test keys, 2.16 million (94.8%) demonstrated consistent behavior across all three engines. In the remaining cases, majority voting identified Firefox as the outlier in several layout-related scenarios involving nested percentages and flexbox behavior.

One notable finding involved discrepancies in length rounding: Firefox uses 1/60 pixel precision for certain layout calculations, while Chromium and WebKit use 1/64 pixels. This difference affected flex item wrapping and scroll width measurements in real-world sites including Slack and Google Store, aligning with reported compatibility issues documented by Mozilla.

The project also explored advanced techniques, including logic programming for margin collapsing, which successfully identified a previously undetected geometry bug across all test cases. Additionally, conformance suites such as WebGPU and Web Audio demonstrated usable coverage rates of 85% and 74.4% respectively when measured against multi-engine agreement.

Bez remains in active development, with ongoing work focused on expanding test coverage, refining generation pipelines, and addressing open questions around feature scope, performance costs, and integration with web specification evolution. The project's source code and documentation are publicly available through its repository, which references external resources including W3C browser specifications, browser compatibility data, and automated test generation tools.