PhantomJS script to check if a web page sniffs the user agent or not.

unsniff.js

// Check if a web page sniffs the user agent or not.

var page = require('webpage').create(),
    sniffing, address;

page.onInitialized = function () {
    page.evaluate(function () {

        window.originalNavigator = window.navigator;

        navigator = JSON.parse(JSON.stringify(window.originalNavigator));
        navigator.sniffing = false;

        navigator.__defineGetter__('userAgent', function() {
            navigator.sniffing = true;
            return originalNavigator.userAgent;
        });
    });
};

if (phantom.args.length === 0) {
    console.log('Usage: unsniff.js <some URL>');
    phantom.exit();
} else {
    address = phantom.args[0];
    console.log('Checking ' + address + '...');
    page.open(address, function (status) {
        if (status !== 'success') {
            console.log('FAIL to load the address');
        } else {
            window.setTimeout(function () {
                sniffing = page.evaluate(function () {
                    return navigator.sniffing;
                });
                if (sniffing) {
                    console.log('The page tried to sniff the user agent.');
                } else {
                    console.log('The page did not try to sniff the user agent.');
                }
            phantom.exit();
            }, 1500);
        }
    });
}