Bez Generates a Browser Engine From Specs: 0.6% of Features Done, 93.0% Untouched

Bez, an open-source project that generates a web rendering engine from specifications and tests, lists 0.6% of features as fully generated and 93.0% as unreached. The numbers are on the project's own page, under the burrito.space account.

Bez follows the same pattern as OpenDLSS-NR, a Vulkan reimplementation of a proprietary system, and shares its question of what is actually verified. It reached Hacker News on Oct. 2, where the thread has 87 points.

What Bez says it does

The page states the goal as "Generate a web rendering engine from specs and tests". A model writes candidate implementations from specification text. Each candidate is run against Chromium, Firefox and WebKit, and code is committed only when the rendering matches the three shipping browsers. The repository is 76% Rust.

The listed aims are complete or tree-shaken builds, fast performance on all devices, easy embedding and quick updates when specs change. The portions of the page fetched here do not name the model that writes the candidates.

Where it stands on Oct. 2

Measure	Figure
Features fully generated	0.6%
Features hand-written	0.3%
Features unreached	93.0%
CSS 2.1 layout rules implemented	9
Recipe cases passing	227

1. Unreached93 %
2. Fully generated0.6 %
3. Hand-written0.3 %

Source: Bez project page on Tangled, accessed 2026-10-02

The three figures account for 93.9% of features, and the page as fetched does not label the remaining 6.1%. The project also reports passing WPT normal-flow pages, the Web Platform Tests category for basic block layout. It has 8 stars and about 1.2k commits across 21 branches.

The finding that is already useful

The comparison step produced one result worth reading even if the engine never ships. Across 699 of 705 comparisons, the page says, "three browsers mostly agree, and the third names the odd one out". When one browser deviates, the other two settle which behaviour counts as correct.

It also found a concrete difference: Firefox rounds with a 1/60px unit, and the page says this causes real web compatibility issues. A spec read alone would not surface that.

What commenters on the thread doubt

Hacker News user nicoburns, who describes three years of browser-engine work, wrote that AI is very far from doing this and that the generated code would be too slow to be useful. User troupo wrote that most web specifications are written in human technical language, not in a machine-readable form.

User esprehn wrote that specs leave behaviour to the user agent in places, and that real web compatibility means doing what Chrome does. That objection sits next to Bez's design, which treats the three shipping browsers as the oracle and so inherits their quirks on purpose.

None of these comments is a measurement. The project has published none that would answer them, such as render time against any of the three engines.

What comes next

The page gives no schedule, and IANA's example.com change is a reminder that behaviour on trivial pages still shifts. The next figure to watch is the unreached share, which stands at 93.0% on Oct. 2.