I'm using countless web applications on a daily basis. Here are 6 URLs you should bookmark immediately.
BTW, I prefer to use URL bookmarks than Chrome extensions. They eat up RAM, which slows down my Macbook.
Facebook Sharing Debugger: https://developers.facebook.com/tools/debug/sharing/
Use it to scrape a fresh version of your blog post if you've just changed the SEO title, the meta description or the featured image, to make sure your post renders properly when shared on Facebook.
Use it to get a rough sense of the traffic generated by any website. An easy way to know where you stand VS your competitors or to verify the claims of someone pinging you for advertising ("We have massive traffic!"). Replace "site.com" by the website you want to research.
Another source to check the authority of a website. Recently, I've been using Similarweb more often than Alexa but it's always worth checking to get additional data. Both Alexa and Similarweb give you a short selection of similar sites and a few backlinks. For a full list of fresh backlinks, I advise you to use ahrefs (read here).
Wondering whether a website you've stumbled upon is using WordPress? It's easy with isitwp. It will even tell you which theme / plugins are used (when not custom).
Google Translate: https://translate.google.com/
I graduated as an interpreter and I'm designing multilingual websites and content marketing campaigns on a daily basis. When I need to quickly check a translation, I'm using Google Translate.
Probably one of the most impressive free translation tools on the internet. It shows you translations in their context, absolutely mandatory if you're a serious about localisation.