--- title: This Month in Ladybird | daily.dev description: Ladybird's February update reveals the browser project removed all Swift code and replaced its LibJS frontend (lexer, parser, AST, scope collector, bytecode... canonical: https://daily.dev/posts/this-month-in-ladybird-jevgsot1j twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: This Month in Ladybird | daily.dev og:description: Ladybird's February update reveals the browser project removed all Swift code and replaced its LibJS frontend (lexer, parser, AST, scope collector, bytecode... og:url: https://daily.dev/posts/this-month-in-ladybird-jevgsot1j og:image: https://api.daily.dev/og/posts/jevGsOT1j.png og:image:alt: This Month in Ladybird og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # This Month in Ladybird **[Ladybird Browser](https://daily.dev/sources/ladybird)** · 8 min read · 0 upvotes · 0 comments ## Summary Ladybird's February update reveals the browser project removed all Swift code and replaced its LibJS frontend (lexer, parser, AST, scope collector, bytecode generator) with a complete Rust reimplementation, built using AI coding agents like Claude Code and Codex under human direction. The new pipeline produces byte-for-byte identical bytecode to the C++ version, verified across over 65,000 tests, and is enabled by default. Beyond the language shift, 347 PRs from 34 contributors landed major text editing and selection improvements, site-specific performance work on Reddit, YouTube, Discord, and X.com, new CSS features (@counter-style, font-optical-sizing, ScrollTimeline, word-break, grid dense packing), partial SVG relayout, redesigned media controls using shadow DOM, and cookie versioning to cut redundant IPC calls for document.cookie access. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### Why did Ladybird remove Swift and rewrite LibJS in Rust? Ladybird abandoned Swift as a second language alongside C++ after adopting it in 2024 because it did not work out for the project, and replaced the LibJS frontend pipeline (lexer, parser, AST, scope collector, and bytecode generator) with a complete Rust reimplementation instead. The rewrite was done using AI coding agents, Claude Code and Codex, under human direction rather than autonomously. _Track how major browser engines rethink their core language stacks by following rewrites like this on daily.dev._ ### How was the Rust rewrite of Ladybird's LibJS verified against the old C++ implementation? The Rust pipeline was verified to produce byte-for-byte identical bytecode output to the previous C++ implementation, checked across 52,898 test262 tests and 12,461 Ladybird-specific tests with zero regressions. It is enabled by default on all platforms, though developers can switch back to the C++ pipeline with LIBJS_CPP=1 or run both in lockstep with LIBJS_COMPARE_PIPELINES=1. _Developers weighing large-scale rewrites can compare verification strategies like this via daily.dev._ ### How does Ladybird's cookie versioning reduce blocking on document.cookie access? Ladybird caches the cookie string in the WebContent process and tracks a shared version counter, so reading document.cookie returns the cached value immediately without inter-process communication when the version hasn't changed. This targets the common case identified by a Chrome team study showing 87% of cookie reads return the same string as before, eliminating hundreds of blocking calls per page load. _Engineers optimizing browser performance internals can find deep dives like this through daily.dev._ --- Tags: [#css](https://daily.dev/tags/css), [#rust](https://daily.dev/tags/rust), [#webassembly](https://daily.dev/tags/webassembly) [View this post on daily.dev](https://daily.dev/posts/this-month-in-ladybird-jevgsot1j) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"This Month in Ladybird","url":"https://daily.dev/posts/this-month-in-ladybird-jevgsot1j","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/this-month-in-ladybird-jevgsot1j"},"datePublished":"2026-08-31T05:54:47.837Z","dateModified":"2026-08-31T05:56:33.981Z","description":"Ladybird's February update reveals the browser project removed all Swift code and replaced its LibJS frontend (lexer, parser, AST, scope collector, bytecode...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/f0d04d597be9efdaf11883698ad30378?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/f0d04d597be9efdaf11883698ad30378?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Ladybird Browser","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Ladybird Browser","logo":"https://media.daily.dev/image/upload/s--gBOjamNh--/f_auto,q_auto/v1788155675/logos/ladybird?_a=BAMAMicg0","url":"https://daily.dev/sources/ladybird"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/this-month-in-ladybird-jevgsot1j","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"css,rust,webassembly","timeRequired":"PT8M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Ladybird Browser","item":"https://daily.dev/sources/ladybird"},{"@type":"ListItem","position":3,"name":"This Month in Ladybird"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/this-month-in-ladybird-jevgsot1j#faq","mainEntity":[{"@type":"Question","name":"Why did Ladybird remove Swift and rewrite LibJS in Rust?","acceptedAnswer":{"@type":"Answer","text":"Ladybird abandoned Swift as a second language alongside C++ after adopting it in 2024 because it did not work out for the project, and replaced the LibJS frontend pipeline (lexer, parser, AST, scope collector, and bytecode generator) with a complete Rust reimplementation instead. 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