Base58 Encoder / Decoder

How it is calculated

In encode mode the text is read as its raw bytes (UTF-8 for non-ASCII characters), and the whole byte sequence is treated as one big base-256 number. That number is rewritten in base 58 with the Bitcoin alphabet 123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz, which leaves out the look-alikes 0, O, I and l. Each leading zero byte becomes a leading 1, so a zero prefix keeps its length. Decode mode reverses this: every character is looked up in the alphabet, the number is rebuilt and the bytes are shown as text, with leading 1s turned back into zero bytes.

Base58 is an encoding, not encryption, and has no padding or + / = signs. The 4-byte checksum of Bitcoin addresses (Base58Check) is neither added nor checked here. Spaces count as characters, so a stray space makes decoding fail, as does any character outside the alphabet. Empty input gives no result.

Common mistakes

• Mixing up Base58 with Base64. The alphabets differ, so a Base64 string pasted in decode mode usually fails because of characters such as 0, O, I, l, + or /.
• Treating the output as secure. Base58 only changes how data is written, and anyone can reverse it.
• Expecting a Bitcoin address to be validated. A real address has a version byte and a 4-byte checksum (Base58Check); this tool only converts the bytes and checks neither. For example, JxF12TrwUP45BMd decodes happily although it is not an address.
• Pasting a Base58 string with a leading or trailing space. The space is not in the alphabet, so decoding gives no result.
• Dropping or adding leading 1 characters. Each leading 1 stands for one zero byte, so 11JxF12TrwUP45BMd decodes to two invisible zero characters followed by Hello World.