Computers move a lot of information through systems built only for plain text: email, web addresses, JSON, HTML. Base64 rewrites any data, including images and accented letters, using just 64 safe characters (A–Z, a–z, 0–9, + and /). The catch is that it makes things about a third bigger.

It isn't encryption. Anyone can decode Base64 in a second, so never use it to hide passwords or secrets. You'll often see it in email attachments, login tokens, and small images embedded directly in web pages as data:image/png;base64,… addresses.

URL-safe Base64 swaps + and / for - and _ so the result can go in a web address, and usually drops the = padding at the end. Decoding here accepts either kind. Text is treated as UTF-8, so accents and emoji survive the round trip. Everything runs in your browser.