Base64 Encode & Decode

Base64, defined in RFC 4648, writes arbitrary bytes using 64 printable ASCII characters: A–Z, a–z, 0–9, + and /. Every group of three bytes (24 bits) is split into four 6-bit numbers, and each number picks one character from the alphabet. When the input length is not a multiple of three, the final group is padded with one or two = signs. The result is always about 33% larger than the input: 4 characters for every 3 bytes.

It exists because many channels were built for text. Email (MIME), data: URLs in HTML and CSS, JSON fields that carry images or certificates, and HTTP Basic authentication headers all use Base64 to move binary data safely. It is not encryption and hides nothing; decoding needs no key.

Base64 encodes bytes, not letters, so text must first be turned into bytes. This tool always uses UTF-8, the encoding the web runs on: é becomes two bytes and an emoji four. The browser's built-in btoa function alone throws an error on any character above U+00FF, which is why naive encoders fail on accents and emoji; here the text goes through TextEncoder first, and decoding reverses it with TextDecoder. If decoded bytes are not valid UTF-8 (an image, a zip file), the tool shows them as hexadecimal instead of garbled text.

Standard Base64 uses + and /, which have meanings in URLs and file names. The URL-safe alphabet from section 5 of RFC 4648 replaces them with - and _, and padding is usually dropped. JSON Web Tokens use exactly this form. The decoder accepts both alphabets and missing padding, so you can paste either.

Choose a file and the tool reads it locally with FileReader and returns its Base64, or a complete data: URL with the file's MIME type ready to paste into an img tag or a CSS background. Inline images save an HTTP request but grow by a third and cannot be cached separately, so they suit small icons rather than photos. For images with a preview and ready-made HTML and CSS snippets, use Image to Base64.