User script to add Eruda to any page. Originally created for Adguard for Android.

ErudaInjector.user.js

// ==UserScript==
// @name        Eruda Injector
// @version     1.9
// @include     *
// @description Injects Eruda onto any page
// @grant       none
// ==/UserScript==

window.addEventListener('load', function () {
  window.erudaParams = { 
    defaults: {
      displaySize: 50,
      transparency: 0.9,
      theme: 'Monokai Pro'
    }
  };
  if (top.location === location && !window.eruda) {
    var script = document.createElement('script');
    script.src = '//cdn.jsdelivr.net/npm/eruda';
    script.onload = function _onload() {
      window.eruda.init(window.erudaParams);
      window.eruda.get('console').config.set('displayIfErr', false);
      window.eruda.get('console').config.set("displayExtraInfo", true);
    };
    document.head.appendChild(script);
    window.setTimeout(function _checkEruda() {
      if (!window.eruda) {
        var src = '//cdn.jsdelivr.net/npm/eruda';
        if (!/eruda=true/.test(window.location) && localStorage.getItem('active-eruda') != 'true') return;
        document.write('<scr' + 'ipt src="' + src + '"></scr' + 'ipt>');
        document.write('<scr' + 'ipt>eruda.init(window.erudaParams);window.eruda.get("console").config.set("displayIfErr", false);window.eruda.get("console").config.set("displayExtraInfo", true);</scr' + 'ipt>');
      }
    }, 5000, false);
  }
}, false);