Base64 Encoder and Decoder

How Base64 encoding works

Base64 writes any data as plain text using 64 characters that survive email, JSON and URLs: A–Z, a–z, 0–9, + and /. The encoder takes the data three bytes (24 bits) at a time and splits them into four groups of 6 bits. Each 6-bit value, from 0 to 63, becomes one character. When the data does not divide evenly into groups of three bytes, the last group is completed with one or two = signs, called padding. That is why Base64 is always about a third longer than the original: every 3 bytes become 4 characters.

Text is first turned into bytes with UTF-8, the encoding used across the web. Hindi, emoji and accented letters are therefore encoded correctly and decode back to exactly the same text. Tools built on the browser's btoa() function fail on such characters; this one does not use it.

The options

• URL-safe alphabet replaces + with - and / with _, as defined in RFC 4648, section 5. Use it when the result goes into a URL, a file name or a token such as a JWT, where + and / have other meanings.
• Remove = padding leaves out the trailing = signs. The decoder can work them out from the length, so formats such as JWT drop them.
• Wrap lines at 76 characters splits the output into lines of 76 characters, the limit for MIME email attachments in RFC 2045. Lines are separated with a line feed (LF).
• Data URI (File mode) puts the media type in front of the Base64, for example data:image/png;base64,iVBORw0…. It can be pasted straight into an HTML src attribute or a CSS url().

Decoding

The decoder accepts both alphabets, with or without padding, and ignores spaces and line breaks, so Base64 copied from emails, logs or source code works as it is. A data URI prefix and the BEGIN and END lines of a PEM block (the format used for certificates and keys) are skipped automatically. When a character cannot be part of Base64, the tool names it, gives its position and can select it in the input box, which makes stray quotes, percent signs or invisible characters easy to find.

In File mode, the type of the decoded file is worked out from its content (the signature in its first bytes), not just from what a data URI claims. PNG, JPG, GIF, WebP, SVG, PDF, ZIP, Word, Excel and PowerPoint files, MP3 and MP4 media, fonts and plain text are recognised and get a matching file extension. Images and text are previewed before you download them.

Base64 is not encryption

Anyone can decode Base64. It only changes how data is written, not who can read it, so it does not protect passwords or personal data. Everything on this page runs in your browser; your text and files are not uploaded.