Base64

What this does

Base64 turns bytes into 64 safe characters, so binary data can travel through systems that only handle text. Encoding makes the data about a third larger.

Base64 is not encryption

Anyone can decode it, with this page or one line of code. Never treat a base64 string as a secret.

URL-safe base64

The standard alphabet uses + and /, which have a meaning in URLs. The URL-safe form swaps them for - and _ and drops the = padding. JSON Web Tokens use it. The decoder here accepts both forms.