Ladybird is a next-generation web browser engine developed from the ground up, free from corporate control or legacy codebases. It targets developers and early adopters seeking a truly independent alternative to Chromium, WebKit, and Gecko. Built with a multi-process architecture and modular libraries inherited from SerenityOS, it prioritizes security through process isolation and standards compliance.
The project leverages a suite of custom-built libraries including LibWeb, LibJS, and LibWasm, and is transitioning to Rust for long-term maintainability. It runs on Linux, macOS, Windows (via WSL2), and other *Nix systems, with an Alpha release planned for 2026. Funded entirely by donations and sponsorships, Ladybird has no user monetization, ads, or data collection.
What You Get
- Multi-process architecture - Separates UI, WebContent, ImageDecoder, and RequestServer into distinct processes to isolate crashes and improve security against malicious web content.
- LibWeb rendering engine - A custom-built, standards-compliant HTML/CSS rendering engine developed from scratch, not derived from Blink, WebKit, or Gecko.
- LibJS JavaScript engine - A standalone JavaScript implementation built for Ladybird, supporting modern ECMAScript features without dependency on V8 or JavaScriptCore.
- LibWasm WebAssembly implementation - Native WebAssembly execution engine built from scratch to ensure compatibility and performance without relying on existing browser engines.
- Process-isolated image decoding and network stack - Image decoding and HTTP/1.1 requests are handled in separate processes to prevent memory corruption and exploitation from malicious media or scripts.
- SerenityOS-derived core libraries - Reuses and extends LibGfx, LibCrypto, LibTLS, LibUnicode, LibMedia, LibCore, and LibIPC from SerenityOS for graphics, cryptography, Unicode, audio/video, and inter-process communication.
- Rust adoption in progress - Actively transitioning core components from C++ to Rust to improve memory safety and long-term maintainability, with AI-assisted code conversion.
- Hand-written assembly interpreter - Custom-built low-level interpreter for performance-critical components, reducing dependency on external toolchains.
Common Use Cases
- Developing a standards-compliant browser engine - Engineers and browser researchers use Ladybird to study and contribute to a clean-slate implementation of web standards without legacy code baggage.
- Testing web standards compliance - Web developers test their sites against Ladybird to identify non-standard behaviors in dominant browsers and ensure cross-engine compatibility.
- Building secure, sandboxed web applications - Security researchers use Ladybird’s process isolation model to analyze and mitigate browser-based exploits in a controlled environment.
- Contributing to open web infrastructure - Volunteers and sponsors support Ladybird to preserve browser diversity and prevent monopolistic control of the web platform by corporate entities.
Under The Hood
Architecture
- Modular Rust-based design with isolated library crates (LibJS, LibRegex, LibUnicode) enforcing clear separation of concerns and reusability
- Smart pointers (RefPtr, WeakPtr) enable safe reference counting and circular dependency resolution without external frameworks
- Ownership semantics and explicit pointer passing replace traditional dependency injection, enhancing testability and reducing global state
- Domain-specific abstractions like Utf8View and Span provide low-level performance optimizations while preserving type safety
Tech Stack
- Native browser engine built entirely in Rust with minimal external dependencies, compiled with LTO and panic aborts for performance
- Comprehensive tooling including Clippy, Ruff, and pre-commit hooks to enforce code quality, formatting, and CI consistency across Rust and Python
- No web frameworks or databases; instead, a self-contained implementation of browser core components from the ground up
Code Quality
- Extensive test suite based on WPT reftests and text-based validations to verify rendering, CSS parsing, and media query behavior
- Test artifacts and expected outputs are cleanly separated from implementation, enabling precise behavior validation
- Consistent naming and structured test expectations align with web standards, improving maintainability and traceability
- Robust error detection through validation of both valid and invalid syntax patterns, ensuring strict specification compliance
What Makes It Unique
- Native implementation of Web API abort signals with full support for all response body readers, ensuring consistent cancellation semantics
- Deep integration of WPT test expectations directly into the rendering engine, creating a living specification that drives development
- Lightweight, modular architecture isolating rendering, networking, and DOM logic into independently testable components
- Built-in user activation tracking for security-sensitive APIs enforced at the engine layer, not as an afterthought
- Zero-dependency core rendering pipeline with custom memory management and layout algorithms optimized for low-resource environments