Bez - a generated web engine# Generate a web rendering engine from specs and tests. Why# 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. Goals# Complete, or tree-shaken. The default build is a complete engine. For uses other than a web browser, a build can instead contain only the web features its content uses: analyse a site or an app, and every feature it never touches is left out of the binary, not just switched off (docs/content-scoped-engine.md). Fast on any device. A smaller engine does less work and needs less memory. Easy to embed. A small engine with a clear API, for apps and devices that today ship all of Chromium or go without. Fastest to update. When a spec or test changes, the affected code is regenerated and re-verified, not rewritten by hand. How it works# flowchart LR spec["spec text"] --> model["model writes
many candidates"] model --> engine["candidate runs
inside the engine"] browsers["Chromium, Firefox,
WebKit (cached)"] --> check{"same boxes,
same places?"} engine --> check check -- no --> model check -- yes --> code["committed as
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". Findings so far# Three browsers mostly agree, and the third names the odd one out. 699 of 705 browser-pair comparisons agreed across 235 documents (commit 3ca7323); all six disagreements were twelve-deep percentage nesting, and majority voting named Firefox the outlier every time. docs/firefox-app-units.md. That Firefox difference is a real web-compat bug. Gecko rounds lengths to 1/60 px where Blink and WebKit use 1/64 px, which makes a flex item wrap only in Firefox or offsetWidth differ by a pixel. Reproductions match Mozilla-diagnosed breakage on Slack, Google Store and Samsung, and Mozilla bug 1719314. experiments/firefox-compat/. The WPT vote table agrees across most of the suite. A stable three-engine majority covers 2,162,676 of 2,282,301 test/subtest keys (94.8%). docs/wpt-votes.md. Script-observable behaviour agrees too. Trace probes under a fake-media profile agree on 15 of 18 engine pairs; the three disagreements are a real platform difference. docs/dump-format.md → "Trace protocol". Conformance suites are usable oracles. Counting a test usable when two of three engines agree: WPT canvas 82.6% (92.7% excluding tentative), Khronos WebGL with dEQP 99.7%, WPT Web Audio 74.4% (85.6% excluding tentative); the WebGPU CTS about 85% for validation and about 50% for numeric execution. docs/conformance-oracles.md, docs/webgpu-cts.md. Logic programming earns a narrow place. Margin collapsing written as Datalog agreed with the browsers on 1195 of 1195 offsets and caught a seeded bug the geometry check missed in all 227 cases. docs/logic-layer.md. The economics hold for a subset of the platform. About 55–60% of engine-relevant compat entries have a usable automated oracle and generatable spec prose; roughly 8–18% have none. docs/platform-economics.md, docs/oracle-coverage.md. An engine scoped to one site's content is designed, and its content analyser has landed. docs/content-scoped-engine.md. Open questions# 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. Sources# browser-specs, every web spec in one repo: https://github.com/w3c/browser-specs web-features, the web platform grouped into features: https://github.com/web-platform-dx/web-features/ browser-compat-data, every piece of the web surface: https://github.com/mdn/browser-compat-data WPT, the web platform tests: https://web-platform-tests.org/ wpt-gen, WPT tests generated from specs: https://github.com/GoogleChromeLabs/wpt-gen webref, machine-readable terms from web specs: https://github.com/w3c/webref