Why Lightpanda’s Browser Is Written in Zig

In the world of web automation, speed and reliability are king. Lightpanda, a browser engineered from scratch to power large‑scale crawlers, needed a language that could deliver low‑level control without the steep learning curve of C++ or the safety‑first friction of Rust. The team turned to Zig—a language that blends the performance of systems programming with a philosophy of explicitness and simplicity.

The Core Requirements

Building a browser that can render JavaScript, manage thousands of concurrent page loads, and extract data in milliseconds demands three things:

1. Uncompromised performance – every microsecond counts when crawling millions of pages.
2. Fine‑grained memory control – short‑lived DOM trees and JavaScript objects must be allocated and freed deterministically.
3. Modern tooling – a build system that handles cross‑compilation, dependency management, and rapid iteration.

Zig offered a sweet spot: it is simple enough for a small team to master quickly, fast in execution, and tool‑friendly thanks to its built‑in build system and C interop.

Why Not C++?

C++ powers the majority of browsers, but its decades‑long evolution has introduced a labyrinth of features—templates, multiple inheritance, and a sprawling standard library. For a lean team, this complexity translates into:

• Multiple ways to solve the same problem – leading to inconsistent code styles.
• Memory‑safety headaches – use‑after‑free bugs and leaks are still common.
• Build system pain – CMake and header dependencies can stall progress.

While C++ remains unbeatable for large, legacy codebases, Zig’s single, clear approach to allocation and compilation removes much of that overhead.

Why Not Rust?

Rust’s ownership model guarantees safety, but it also imposes a borrow checker that can be unforgiving when dealing with the dynamic, garbage‑collected world of a browser engine. The need to write unsafe blocks for V8 bindings, DOM manipulation, and JavaScript runtime integration quickly erodes Rust’s benefits. Zig sidesteps this by:

• Explicit allocators – every allocation is tied to a known allocator.
• No hidden control flow – pointers are non‑null by default, and the compiler warns against misuse.
• Safe escape hatches – unsafe is still available, but its ergonomics are less punitive.

Zig’s Key Features in Action

Explicit Memory Management

Zig’s allocator model forces developers to decide exactly how memory is allocated. A typical page load in Lightpanda looks like this:

const std = @import("std");

pub fn loadPage(_allocator: std.mem.Allocator, url: []const u8) !void {
    var arena = std.heap.ArenaAllocator.init(_allocator);
    defer arena.deinit();

    const allocator = arena.allocator();
    const dom_tree = try parseDom(allocator, url);
    const css_rules = try parseStyles(allocator, dom_tree);
    const js_context = try createJsContext(allocator);

    try executePage(js_context, dom_tree, css_rules);
}

Each page gets its own arena; when the page finishes, the entire arena is released in one operation—no GC pauses, no reference counting.

Compile‑Time Metaprogramming

Zig’s comptime feature allows code to run during compilation, enabling automatic binding generation for V8. Instead of writing boilerplate glue for each native type, the compiler introspects structs and emits JavaScript wrappers on the fly:

const Point = struct {
    x: i32,
    y: i32,
    pub fn moveUp(self: *Point) void { self.y += 1; }
    pub fn moveDown(self: *Point) void { self.y -= 1; }
};

runtime.registerType(Point, "Point");

This eliminates manual glue code and keeps the language surface small.

First‑Class C Interop

V8 is a C++ library, but Zig can import C headers generated by rusty_v8 and call into them directly. For example, Lightpanda uses libcurl for HTTP requests:

pub const c = @cImport({
    @cInclude("curl/curl.h");
});

Because Zig’s interop is first‑class, the team can leverage the vast ecosystem of existing C libraries without writing adapters.

Built‑In Build System

Zig’s build system, written in Zig, abstracts away the pain of cross‑compilation and dependency management. A minimal build.zig for libcurl looks like:

fn buildCurl(b: *Build, m: *Build.Module) !void {
    const curl = b.addLibrary(.{ .name = "curl", .root_module = m });
    curl.addIncludePath("vendor/curl/include");
    curl.addCSourceFiles(.{ .files = &.{ "vendor/curl/src/libcurl.c" } });
}

All configuration lives in one place, making the developer experience smoother than CMake or Meson.

Fast Compile Times

While Zig isn’t a drop‑in replacement for Go’s instant compilation, its rebuild times are competitive—under a minute for a full project. The Zig team is actively working on a native backend that promises even faster incremental builds.

The Takeaway

After months of iteration, Lightpanda’s creators found Zig to be a productive and performant choice for a browser that must be both fast and easy to maintain. Key lessons include:

• Simplicity pays – a language that forces explicit decisions reduces hidden bugs.
• Allocator discipline – arenas give predictable memory usage and eliminate GC overhead.
• Community support – despite being pre‑1.0, Zig’s ecosystem is growing fast, with active Discord channels and a robust standard library.

For teams looking to build a specialized browser or any performance‑critical system, Zig offers a compelling alternative to the traditional C++/Rust stack.

Source: Lightpanda Blog – Why We Built Lightpanda in Zig