How Microsoft created EdgeHTML, the rendering engine powering the Spartan browser
Inside Microsoft's New Rendering Engine For The “Project Spartan” — Last week, Microsoft made its biggest announcement for the web since it first introduced Internet Explorer in 1995: a new browser, codenamed “Project Spartan31.”
Context & Ripple Effects
The arc runs fast: weeks after sources leaked a lightweight browser codenamed Spartan for Windows 10, Microsoft confirmed the bigger news underneath it — Spartan would ship with an entirely new rendering engine, EdgeHTML, built alongside but separate from the Trident codebase that Internet Explorer has used since 1995.
The strategy detail matters as much as the engineering: per Microsoft's own Windows 10 browser split, Spartan carries the Edge engine while IE 11 keeps Trident, letting the new browser drop two decades of legacy compatibility rather than carry it forward. The MSDN build writeup frames this as a ground-up rebuild aimed at interoperability instead of IE-specific quirks.
First-order effects
- Web developers gain a fourth major rendering engine to test against overnight, with Edge initially positioned as standards-first and free of the IE compatibility modes they have spent years coding around.
Second-order effects
- Rival engines now face a benchmark comparison instead of a legacy excuse — by July, testing showed Edge performing on par with competitors in most suites with outsized WebGL gains, putting pressure back on Chrome and Firefox rather than letting them coast on IE's reputation.
Third-order effects
- Decoupling the modern browser from IE's compatibility burden — including dropping ActiveX entirely and shipping on every Windows 10 device — points toward browsers as independently updatable platforms rather than OS-bound components.
The trend: Browser engines are re-separating along modern-standards versus legacy-compatibility lines, with Windows 10 forcing Microsoft to run both tracks at once.