Base64 кодирование онлайн

Base64 Encoding and Decoding Online

Base64 is a binary-to-text encoding scheme using 64 printable characters (A-Z, a-z, 0-9, +, /). Encoding increases data size by ~33% but allows safe transmission of binary data through text protocols: email, JSON, XML, HTML.

How Base64 Encoding Works

The algorithm splits input bytes into groups of 3 (24 bits), then each group is divided into 4 six-bit values (0–63). Each value is replaced with a character from the Base64 alphabet. If input is not a multiple of 3 bytes, the result is padded with = characters.

Where Base64 Is Used

• Data URI — embedding images in HTML/CSS: data:image/png;base64,...
• Email (MIME) — attachments are Base64-encoded for SMTP transmission
• JWT tokens — header and payload are Base64url-encoded
• APIs — transmitting binary data in JSON fields
• Basic Auth — HTTP Authorization header contains login:password in Base64

Encoding Overhead

Base64 increases data size by exactly 33.3% (3 bytes → 4 characters). Our tool shows original size, encoded size, and overhead percentage in real time.

Frequently Asked Questions

Is Base64 encryption?
No. Base64 is encoding, not encryption. Anyone can decode a Base64 string without a key.

Why is padding (= symbols) needed?
Padding aligns the result length to a multiple of 4. One = means 2 input bytes, two == means 1 input byte.

What is the difference between Base64 and Base64url?
Base64url replaces + with - and / with _, removes padding. Used in JWT, URL parameters, and filenames.

Is it safe to use?
Yes, all operations run in your browser. No data is sent to a server.

For decoding use the Base64 decoder, for images — Image to Base64, for JWT analysis — JWT decoder.