Base64 Encoding and Decoding: A Developer's Reference

What is Base64?

Base64 is a way to represent binary data using only printable text characters. It converts any sequence of bytes into a string made up of 64 safe characters: the uppercase and lowercase letters A–Z, the digits 0–9, and the symbols + and /. A = character is used for padding at the end when needed.

It's important to understand that Base64 is encoding, not encryption. Anyone with the encoded string can decode it instantly. It's used to safely carry binary data through systems that only handle text — not to protect data.

Where you'll encounter Base64

• Data URLs — images embedded directly in HTML or CSS as data:image/png;base64,iVBOR...
• Basic Authentication — HTTP headers carry username:password encoded as Authorization: Basic dXNlcjpwYXNz
• JWT tokens — the header and payload sections of a JWT are Base64URL-encoded (a variant that uses - and _ instead of + and /)
• Email attachments — the MIME standard uses Base64 to encode binary file attachments in email messages
• Binary data in JSON — when you need to include image or file data inside a JSON payload

Encode and decode instantly

Use our Base64 Encode/Decode tool for quick conversions. It handles Unicode text including emoji and international characters correctly.

Base64 and JWTs

JWT tokens use Base64URL encoding — a slightly modified version of standard Base64 that's safe for use in URLs and HTTP headers. Our JWT Decoder handles this variant correctly and shows you the full decoded payload including all claims and timestamps.

Why Base64 makes data larger

Base64 encodes every 3 bytes of input as 4 text characters. This results in approximately 33% larger output than the original binary. This size increase is the trade-off for making binary data safe to transmit in text-only contexts.