Base64

About this Base64 encoder

Base64 maps every three bytes of input onto four characters drawn from a 64-symbol alphabet. Because four characters carry the information of three bytes, the encoded text is about 33% larger than the original — a 3 MB image becomes roughly 4 MB of text. That expansion is the price of moving binary data through channels that only accept printable ASCII, such as JSON, XML or an email header.

The classic failure of naive Base64 tools is non-ASCII text. The browser's btoa() function only accepts characters in the Latin-1 range, so calling it directly on Chinese, Cyrillic or emoji produces either an exception or mojibake. This page encodes your string to UTF-8 bytes first and then Base64-encodes those bytes, and reverses that order on decode, so multi-byte text survives the round trip intact.

Base64URL is a variant used by JWTs and OAuth, defined in RFC 4648 §5. It substitutes - for + and _ for / so the result is safe inside a URL path, and it usually drops the = padding. Decoding here accepts either alphabet, so you can paste a token segment without adjusting it first. Remember that Base64 is an encoding, not encryption: it provides no confidentiality whatsoever.