Bez: Generating a browser engine from specs and tests

Generate a web rendering engine from specs and tests.

Building a web engine by hand costs hundreds of engineers and many years, so only a few companies can have one, and only they decide how the web works. Bez generates the engine instead: from the specifications, with the three shipping browsers (checked against each other) and WPT as the tests. Once the pipeline exists, each extra engine costs very little.

flowchart LR spec["spec text"] --> model["model writes<br/>many candidates"] model --> engine["candidate runs<br/>inside the engine"] browsers["Chromium, Firefox,<br/>WebKit (cached)"] --> check{"same boxes,<br/>same places?"} engine --> check check -- no --> model check -- yes --> code["committed as<br/>ordinary Rust"]

docs/generation-loop.md — how one rule goes from spec text to committed code.

docs/geometry-verification.md — how the engine's layout is checked against three browsers.

docs/generated-functions.md — the layout rules generated so far and what each batch showed.

roadmap.md — the plan, the decisions and the open questions.

Status#

Computed against browser-compat-data 8.0.4 (17259 leaf keys, 74 rules in docs/feature-map.json) on 2026-09-25.

See docs/dashboard.md for what these statuses mean and how this table is kept in sync.

DOM, style, box tree and fragment tree are hand-written in crates/dom and crates/layout and pass their browser checks (roadmap.md → "Phase 1 — Engine bootstrap"). Nine CSS 2.1 layout rules live in crates/layout/src/generated; eight were written by models and admitted against the three-browser vote, and block height keeps its hand-written rule because no model candidate beat it. Together they pass all 227 recipe cases and all 11 usable WPT normal-flow pages. Which rules the engine actually calls: roadmap.md → "Which resolver each generated function runs". What would prove the thesis: roadmap.md → "Proof of concept".

What building each rule costs by hand, how wide a feature's generated part should be, how much of WPT is reachable without JavaScript, and where IDL-generated code ends: roadmap.md → "Open questions". Area-by-area status: docs/platform-areas.md.