Encode and decode Base64 in both directions, with correct handling of Unicode and emoji and a URL-safe variant that swaps the problematic characters. Everything runs locally in your browser, so nothing you paste is transmitted.
No, and this matters. Base64 is a reversible encoding with no key, so anyone can decode it instantly. It exists to move binary data safely through text-only channels, not to hide anything. Never use it to protect a secret.
A variant that replaces + with - and / with _, because the standard characters have special meaning in URLs. Padding with = is often dropped too. It is what JSON Web Tokens use.
It packs 3 bytes into 4 characters, so output is about 33% larger than the input, plus padding. That is the cost of restricting yourself to a safe character set.