My starting point for Violentmonkey userscripts

template.user.js

// ==UserScript==
// @name        Website tweaks
// @version     1.4
// @author      Antonio Bueno <[email protected]>
// @namespace   userscripts.atnbueno.com
// @match       http://www.example.com/*
// @require     https://cdn.jsdelivr.net/npm/jquery@3/dist/jquery.min.js
// @require     https://cdn.jsdelivr.net/npm/toastify-js
// @resource    toastifyCSS https://cdn.jsdelivr.net/npm/toastify-js/src/toastify.min.css
// @grant       GM_addStyle
// @grant       GM_getResourceText
// ==/UserScript==

(function () {
    "use strict";

    /*
     * DOM manipulations courtesy of jQuery
     */

    // Modificacions are applied once the DOM has been build (images may be still loading)
    $(document).ready(function () {

        // Makes clear that the script is running and its version
        notification(GM.info.script.name + " " + GM.info.script.version, "hello", 3);

        // Technical info to console
        console.log(GM.info);

        /* Your code here */

    });

    /*
     * Notifications courtesy of Toastify JS (see https://apvarun.github.io/toastify-js/)
     */

    GM_addStyle(GM_getResourceText("toastifyCSS") + `
        div.toastify { margin: inherit; padding-bottom: 20px; width: inherit; font-family:
            -apple-system, system-ui, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif }
    `);
    function notification(message, type = "info", timeout = 5) {
        // The "type" parameter accepts four values: "info", "warning", "error" and "hello"
        // The "timeout" parameter is expressed in seconds although Toastify uses milliseconds
        var color, icon;
        switch (type) {
            case "warning": color = "rgba(201, 201, 0, 0.8)"; icon = "⚠️"; break;
            case "error": color = "rgba(201, 51, 51, 0.8)"; icon = "🛑"; break;
            case "hello": color = "rgba(51, 153, 51, 0.8)"; icon = "👋🏼"; break;
            default: color = "rgba(51, 51, 153, 0.8)"; icon = "ℹ️\uFE0F ";
        }
        Toastify({ text: icon + " " + message, duration: timeout * 1000, gravity: "bottom", style: { background: color } }).showToast();
    }

})();