Base64
Binary data wearing a text costume.
Where it came from
Base64 comes from PEM (1987) and early email: SMTP could only carry 7-bit ASCII, so binary attachments needed a text costume. MIME standardized it in 1992–1996, and the web reused it for Data URIs, JWT tokens and CSS-embedded images.
How it works
Take 3 bytes (24 bits), split into four 6-bit groups, map each 0–63 value onto the alphabet A–Z a–z 0–9 + /. When the input isn't divisible by 3, `=` padding fills the tail — that's why Base64 strings often end with one or two equals signs.
Size grows ~33% (4 characters per 3 bytes). The URL-safe variant swaps `+/` for `-_` so tokens survive in URLs without percent-encoding.
Decoding is pure math — UWC does it instantly, UTF-8 safe, entirely offline.
Encode & decode Base64
Paste text or a Base64 blob — conversion runs locally, safe for secrets you'd rather not upload anywhere.