Base64 Encoder and Decoder Online

Base64 is an encoding, not encryption. Anyone can read what you produce with it, and it is trivially reversible. Do not use it to protect a password, an API key, or anything else sensitive — it provides no confidentiality whatsoever.

The interesting problem is Unicode. Base64 operates on bytes, but text in a browser is UTF-16 code units. Naive implementations encode the code units rather than the underlying bytes, which corrupts anything outside ASCII — accented characters, emoji, and non-Latin scripts all come back wrong. This tool encodes UTF-8 bytes explicitly, so a string round-trips exactly.

Base64 output is 33% larger than the input, plus padding. That expansion is inherent to the scheme, which maps 6 bits onto an 8-bit character because it wants to use only printable ASCII. If size matters, compress first and then Base64 the result.

Decoding validates its input. Characters outside the Base64 alphabet, or a padding run in the wrong place, produce an error rather than a string full of replacement characters, so a corrupt payload is visible instead of silently mangled.

A common use is embedding binary data in a JSON payload or an HTTP header, neither of which tolerate arbitrary bytes. Another is carrying small credentials in a URL-safe form — though for that, Base64url is the correct variant because standard Base64 uses + and /, both of which need escaping in a URL.