Helix

Helix is a web browser written from scratch in C++17, with its own HTML parser, DOM, CSS engine, JavaScript engine, layout engine, and renderer. No Chromium, no WebView2, no CEF, no QtWebEngine. Everything that makes it a browser is hand-built.

It runs on Windows, macOS, and Linux from a single shared engine, with a thin native shell on each platform.

What's built from scratch

• HTML: tokenizer with 170+ named entities, tree-construction parser with implicit element creation, auto-close rules, foster parenting, scope-aware end tags, and formatting element adoption (864 lines)
• CSS: 90+ properties, cascade with combinators, attribute selectors, :is()/:where(), @supports, custom properties (var()), media queries, calc()/clamp()/min()/max(), viewport units, box-sizing, object-fit, flexbox (wrap/shrink/basis/align-self), grid, tables, floats, positioning with percentage offsets, text-align (incl. justify), text-indent, text-decoration, vertical-align, linear-gradient(), box-shadow, transform (translate/scale/rotate), overflow: auto/scroll, :hover/:focus/:checked/:disabled/:enabled, :nth-child(), :not(), and ~ selectors, and more
• JavaScript: lexer, parser, bytecode compiler, VM with 260+ native functions. Supports classes, destructuring, template literals, async/await, optional chaining (?.), nullish coalescing (??), for...of, real RegExp via <regex>, fetch(), getComputedStyle(), DOM geometry APIs, observer APIs, addEventListener with event bubbling, and external <script src> loading
• SVG: rasterizer for inline and external SVG images. Supports rect/circle/ellipse, line/polyline/polygon, path commands (M/L/H/V/C/S/Q/T/A/Z), text/tspan, nested <svg>, <g>, defs/<use>/symbol reuse, linear/radial gradients, viewBox and preserveAspectRatio, transforms, CSS class/style rules, opacity, stroke dash arrays, line caps/joins, fill rules, and all CSS named colors
• Layout: block, inline (with line breaking), float, table (auto column sizing), flex (row/column, wrap, shrink, basis, align-self, justify-content, gap), grid (column tracks), positioned (static/relative/absolute/fixed with % offsets)
• Rendering: per-platform painter, DPI-aware, HiDPI scaling
• Forms: interactive <input>/<textarea> with typing, cursor, and GET submission
• Auto-updater: checks GitHub releases on startup, downloads in background, one-click F12 to apply and restart
• Tabs, per-tab history, zoom, find-in-page, async image loading (6 concurrent)

Dependencies

Only three things are not hand-written:

• libcurl: HTTP/HTTPS and TLS (you don't hand-roll TLS)
• stb_image: JPEG/PNG/etc. decoding (vendored single header)
• OS drawing APIs: Direct2D + DirectWrite (Windows), Core Graphics + Core Text (macOS), GTK3 + Cairo + Pango (Linux). These only plot pixels, glyphs, and bitmaps; all layout and paint logic is Helix's own.

Build

Requires CMake 3.20+ and a C++17 compiler. The version is derived automatically from the latest git tag. libcurl is downloaded via CMake if a system copy isn't found.

Windows

Visual Studio build tools with the x64 C++ toolchain.

build.bat

build\Release\Helix.exe

macOS

Xcode command line tools.

cmake -B build
cmake --build build
open build/Helix.app

Linux

GTK3 development headers (and ideally system libcurl):

sudo apt-get install -y build-essential cmake libgtk-3-dev libcurl4-openssl-dev pkg-config
cmake -B build
cmake --build build
./build/Helix

Releases

Prebuilt binaries for all three platforms are published on the Releases page, built by CI on every tag. Helix auto-updates: on startup it checks for a newer release and downloads it in the background. Press F12 when the status bar shows an update is ready to apply it instantly.

Keyboard shortcuts

Shortcut	Action
Ctrl+L	Focus address bar
Ctrl+T / Ctrl+W	New / close tab
Ctrl+R / F5	Reload
Ctrl+F	Find in page
Ctrl+G / Ctrl+Shift+G	Find next / previous
Ctrl++/-	Zoom in/out
Alt+Left/Right	Back / forward
F12	Apply pending update

Running engine tests

build\Release\helix-tests.exe html
build\Release\helix-tests.exe css
build\Release\helix-tests.exe layout
build\Release\helix-tests.exe paint
build\Release\helix-tests.exe js
build\Release\helix-tests.exe network

Fixtures live under tests/fixtures. Each has an input file and an expected text snapshot. When engine behavior changes intentionally, change the implementation first, inspect the failing output, then update the snapshot only once the new behavior is correct.

Diagnostics

Two offline tools render without the GUI, useful for debugging:

build/dump_layout page.html [viewportWidth]   # prints the box tree + geometry
build/dump_js script.js                       # runs the JS engine