Base64 Encoder and Decoder [2025]

Base64 is a binary-to-text encoding scheme that represents binary data in a printable ASCII string format. It's commonly used to encode data that needs to be transmitted over media designed to handle text, such as email or URLs.

The standard Base64 alphabet uses 64 characters: A-Z, a-z, 0-9, +, and /. URL-safe Base64 replaces + and / with - and _, respectively, and may omit padding characters.

Base64 Alphabet

The standard Base64 alphabet consists of:

• • A-Z (uppercase letters)
• • a-z (lowercase letters)
• • 0-9 (digits)
• • + and / (symbols)
• • = (padding character)

URL-Safe Base64 Alphabet

The URL-safe Base64 alphabet consists of:

• • A-Z (uppercase letters)
• • a-z (lowercase letters)
• • 0-9 (digits)
• • - and _ (symbols)

Encoding Process:

1. The input data is converted into a stream of bytes.
2. The byte stream is grouped into sets of 3 bytes (24 bits).
3. Each 24-bit group is divided into four 6-bit groups.
4. Each 6-bit group is mapped to a character in the Base64 alphabet.
5. If the input is not a multiple of 3 bytes, padding ('=') is added.

Decoding Process:

1. The input data is converted to base64 with padding.
2. Each Base64 character is converted to its 6bit binary representation.
3. The binary data is concatenated.
4. The concatenated binary data is converted back into octets.
5. Each octet is represented as a UTF-8 character.