Extensions
The same engines, where you already are. Select something, right click, and every reading of it appears beside what you were reading.
What they do
Select a UUID, a cron expression, a colour, a timestamp, a measurement or a date, and the panel shows what it is and what follows from it. Where something has several true readings, you get all of them: 1066 is a number, a year and a colour, and nothing picks for you. Every value that points at another object is a link, so you can walk from a number to its square, from an address to its network, or from a formula to its elements without typing anything.
They contain no answers
Neither extension knows what a UUID is. Both call the public API, so there is one implementation of what an input means and they cannot disagree with this site. An engine added here appears in both without an update.
What leaves your machine
The text you select, when you ask for it and at no other time. Nothing else on the page or in the file is read, and the Chrome extension holds no permission that would let it read one. There is no account, no key and no cookie. This site records which kinds of thing were recognised and how many bytes were sent, never the text itself. Selections over 10 KB are refused before anything is sent.
So do not nerdulate anything confidential, for the same reason you would not paste it into a search box. The privacy page has the detail.
Free, and quietly so
No adverts, no upsell, no telemetry of their own, and nothing to sign up for. They are both free during the API beta, which has no key and no rate card.