Bez Project Generates Web Rendering Engine from Specifications and Tests

Automated Web Engine Generation

The Bez project is an initiative to generate web rendering engines automatically. Instead of manual development, which requires extensive engineering resources and time, Bez uses web specifications and existing browser tests (like WPT) to create an engine. This method seeks to lower the barrier to entry for web engine development, which is currently dominated by a few large companies.

Project Goals and Benefits

Key goals for Bez include generating complete or tree-shaken engines, allowing for smaller binaries tailored to specific content by omitting unused features. This approach is intended to result in faster performance on various devices due to reduced workload and memory footprint. Additionally, Bez aims for easy embeddability with a clear API, making it suitable for applications and devices that currently either ship full Chromium or lack a web engine. The generation process also promises faster updates, as changes in specifications or tests can trigger regeneration and re-verification of affected code rather than manual rewrites.

How the Generation Process Works

The process involves converting specification text into models that generate multiple candidate engine implementations. These candidates are then run within the engine and checked against the rendering outputs of Chromium, Firefox, and WebKit. If the candidate engine produces the same visual results, the generated code is committed, primarily in Rust. This iterative verification ensures compliance with established browser behaviors.

Current Status and Progress

As of September 25, 2026, Bez has computed against browser-compat-data 8.0.4. Core components like DOM, style, box tree, and fragment tree are hand-written and pass browser checks. Nine CSS 2.1 layout rules have been generated, with eight admitted after model-based generation and verification against the three major browsers. These rules collectively pass all 227 recipe cases and 11 usable WPT normal-flow pages, demonstrating initial success in automating complex layout logic.