use JavaScript to detect GPU used from within your browser

webgl-detect-gpu.js

var canvas = document.createElement('canvas');
var gl;
var debugInfo;
var vendor;
var renderer;

try {
  gl = canvas.getContext('webgl') || canvas.getContext('experimental-webgl');
} catch (e) {
}

if (gl) {
  debugInfo = gl.getExtension('WEBGL_debug_renderer_info');
  vendor = gl.getParameter(debugInfo.UNMASKED_VENDOR_WEBGL);
  renderer = gl.getParameter(debugInfo.UNMASKED_RENDERER_WEBGL);
}

// Sample output:
//
// » console.log(renderer);
// ATI Technologies Inc. AMD Radeon R9 M370X OpenGL Engine