Base64 Encoder/Decoder

Base64 is an encoding scheme that represents binary data using a limited set of printable text characters. The reason it remains everywhere in 2026 is practical: many transport mediums were built to carry text, not arbitrary bytes. Email attachments, web API payloads, and images embedded directly inside HTML documents all lean on it to move binary content through text-only channels without corruption.

Encoding works in fixed groups. Three bytes of input form 24 bits, which split evenly into four 6-bit blocks, and each block maps to one character from the Base64 alphabet of A-Z, a-z, 0-9, plus the symbols + and /. When the input length is not a multiple of three, padding characters (=) fill the gap. Decoding simply runs the chain backward, translating each character into its 6-bit value, regrouping those bits into 8-bit bytes, and reconstructing the original data.

Two details trip people up. First, encoded output runs roughly 33% larger than the source, so it has a real cost in bandwidth and storage that matters at scale. Second, the alphabet is not universal: standard Base64 uses + and /, while the URL-safe variant swaps them for - and _. Mixing the two is one of the most frequent causes of failed decodes in API integrations, so confirm both ends agree on the character set before sending anything across the wire.