Paste something, press Encode or Decode. Nothing is uploaded; it all happens in this tab.
Input
Empty
Output
Empty
That looks like a JWT. Its header and payload are Base64 URL-safe.
How to use it
Pick a format at the top: Base64, Base64 URL-safe, Hex, URL encoding or HTML entities.
Paste into Input, or press Sample to see one.
Press Encode or Decode. From the keyboard, Cmd or Ctrl with Enter encodes; add Shift to decode.
Copy the output, save it as a file, or press Use as input to go round again.
Pasted a JWT? Press Decode the JWT to read its header and payload and see whether it has expired.
What the formats are for
Base64 carries bytes through things that only accept text, like JSON or an email. URL-safe Base64 is the same with - and _ instead of + and /, so it survives inside a URL. Hex writes each byte as two characters. URL encoding escapes characters that have a meaning in a URL. HTML entities escape characters that would otherwise be read as markup.
None of these is encryption. Anyone can decode them, so they hide nothing. Text is read and written as UTF-8.