Base64 Encoder / Decoder

What is Base64?

Base64 is a binary-to-text encoding scheme that represents binary data using 64 printable ASCII characters (A–Z, a–z, 0–9, +, /). It is defined in RFC 4648 and widely used for embedding binary content in text-based formats.

• Every 3 bytes of input become 4 Base64 characters
• Output is padded with = to a multiple of 4 characters
• ~33% size overhead compared to raw binary

Standard vs URL-safe

Standard Base64 uses + and / which are special characters in URLs. The URL-safe variant (RFC 4648 §5) replaces them with - and _ and omits padding, making it safe to embed in URLs without percent-encoding.

• Standard: uses + / with = padding
• URL-safe: uses - _, no padding
• Used in JWTs, OAuth tokens, and URL parameters

Common uses

• Email (MIME) — encode binary attachments as ASCII text
• Data URIs — embed images and fonts inline in HTML/CSS
• JWTs — header and payload are Base64url-encoded JSON
• HTTP Basic Auth — Authorization: Basic <base64(user:pass)>
• Cryptography — encode keys, certificates, and signatures