Stops fingerprinting scripts from testing 3000+ fonts by faking layout results after 200 probes. Includes metric spoofing and font stability per session.
// ==UserScript==
// @name Anti Font Fingerprinting (Limited Probes)
// @namespace http://tampermonkey.net/
// @version 2.1
// @description Stops fingerprinting scripts from testing 3000+ fonts by faking layout results after 200 probes. Includes metric spoofing and font stability per session.
// @author Atom
// @match *://*/*
// @grant none
// @run-at document-start
// ==/UserScript==
(function() {
'use strict';
// Exclude trusted domains if needed
const excludeSites = [
"gmail.com", "outlook.com", "notion.so", "office.com", "figma.com"
];
const currentHost = location.hostname;
if (excludeSites.some(site => currentHost.includes(site))) return;
const randomOffset = () => (Math.random() - 0.5) * 2;
const MAX_FONT_PROBES = 200;
let fontProbeCount = 0;
// Monkey patch getBoundingClientRect to limit effectiveness of font testing
const originalGetBoundingClientRect = Element.prototype.getBoundingClientRect;
Element.prototype.getBoundingClientRect = function(...args) {
const tag = this.tagName.toLowerCase();
const font = this.style?.fontFamily?.toLowerCase?.() || "";
const isHidden = this.offsetParent === null || this.offsetWidth === 0;
const likelyProbe = tag === "span" && font && isHidden;
const rect = originalGetBoundingClientRect.apply(this, args);
if (likelyProbe) {
fontProbeCount++;
if (fontProbeCount > MAX_FONT_PROBES) {
// Return fake, constant rect to break detection
return {
...rect,
width: 100,
height: 10,
top: 0, left: 0, bottom: 10, right: 100,
x: 0, y: 0,
toJSON: rect.toJSON.bind(rect)
};
}
}
// Otherwise slightly randomize
return {
...rect,
width: rect.width + randomOffset(),
height: rect.height + randomOffset(),
x: rect.x + randomOffset(),
y: rect.y + randomOffset(),
top: rect.top + randomOffset(),
left: rect.left + randomOffset(),
right: rect.right + randomOffset(),
bottom: rect.bottom + randomOffset(),
toJSON: rect.toJSON.bind(rect)
};
};
// Same for offsetWidth / offsetHeight
const patchOffset = (prop) => {
const descriptor = Object.getOwnPropertyDescriptor(HTMLElement.prototype, prop);
Object.defineProperty(HTMLElement.prototype, prop, {
get: function() {
const font = this.style?.fontFamily?.toLowerCase?.() || "";
const tag = this.tagName.toLowerCase();
const isHidden = this.offsetParent === null || descriptor.get.call(this) === 0;
const likelyProbe = tag === "span" && font && isHidden;
if (likelyProbe) {
fontProbeCount++;
if (fontProbeCount > MAX_FONT_PROBES) {
return prop.includes("Width") ? 100 : 10;
}
}
return descriptor.get.call(this) + randomOffset();
},
configurable: true
});
};
patchOffset("offsetWidth");
patchOffset("offsetHeight");
// Patch Canvas measureText
const originalMeasureText = CanvasRenderingContext2D.prototype.measureText;
CanvasRenderingContext2D.prototype.measureText = function(text) {
const metrics = originalMeasureText.apply(this, arguments);
return {
...metrics,
width: metrics.width + randomOffset(),
actualBoundingBoxLeft: metrics.actualBoundingBoxLeft + randomOffset(),
actualBoundingBoxRight: metrics.actualBoundingBoxRight + randomOffset(),
actualBoundingBoxAscent: metrics.actualBoundingBoxAscent + randomOffset(),
actualBoundingBoxDescent: metrics.actualBoundingBoxDescent + randomOffset()
};
};
// Optional: Hide document.fonts completely (not used by browserleaks, but useful elsewhere)
Object.defineProperty(document, 'fonts', {
get: () => ({
forEach: () => {},
ready: Promise.resolve(),
add: () => {},
delete: () => {},
clear: () => {},
size: 0
}),
configurable: true
});
console.log("[Anti-Fingerprint] Font probe limiter active. Max probes:", MAX_FONT_PROBES);
})();