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Base64 Decoder and Encoder

This Base64 decoder and encoder reads Base64 as text, or switches to Encode to turn text into Base64. It works with UTF-8 and with the URL-safe alphabet.

Runs in your browser. Your text is not sent to a server. Sources: RFC 4648 Updated

Direction
20 characters
13 characters

13 bytes out

How Base64 encoding works: 3 bytes, 4 characters

Base64 takes the bytes three at a time. Three bytes are 24 bits, which are cut into four groups of 6 bits. Each group is a number from 0 to 63 and is written as one character from this alphabet:

0–25: A–Z    26–51: a–z    52–61: 0–9    62: +    63: /

Text is turned into UTF-8 bytes first; the text to hex converter shows those bytes for any text. Decoding reverses the steps and then reads the bytes as UTF-8.

How to encode text to Base64 by hand

Encoding Hi!:

  1. The bytes are 72, 105 and 33. In binary, as text to binary writes them: 01001000 01101001 00100001
  2. Regrouped into sixes: 010010 000110 100100 100001
  3. As numbers: 18, 6, 36, 33. In the alphabet these are S, G, k and h.
  4. Result: SGkh

When the input does not divide by three, the last group is padded: Hi encodes to SGk= and H to SA==.

Diagram of Base64 encoding of "Hi!": the bytes 72, 105 and 33 become 24 bits, cut into the 6-bit numbers 18, 6, 36 and 33, which are the characters S, G, k and h, so the result is SGkh.
Four characters for every three bytes is why Base64 is about a third larger than the data it carries.

Base64 examples: text, JSON, accents and emoji

TextBase64URL-safe
Hello, World!SGVsbG8sIFdvcmxkIQ==SGVsbG8sIFdvcmxkIQ
user:passworddXNlcjpwYXNzd29yZA==dXNlcjpwYXNzd29yZA
{"alg":"HS256"}eyJhbGciOiJIUzI1NiJ9eyJhbGciOiJIUzI1NiJ9
caféY2Fmw6k=Y2Fmw6k
a>b?cYT5iP2M=YT5iP2M
😀8J+YgA==8J-YgA

What the Base64 decoder accepts

  • The standard alphabet and the URL-safe alphabet, also mixed.
  • Missing padding, and line breaks or spaces inside the data.
  • A data:…;base64, prefix, which is ignored.

It reports the first character that is not part of Base64, and a length that cannot be right (a single leftover character can never be decoded).

If the decoded bytes are a picture, the Base64 to image converter shows it and saves it as a file. Text full of percent signs, such as hello%20world, is URL encoding, not Base64: read it with the URL decoder.

Base64 Decoder and Encoder: FAQ

What is Base64 used for?
For carrying bytes through systems that only handle text. Email attachments, images embedded in HTML or CSS as data URLs, and the parts of a JSON Web Token are common examples.
Is Base64 encryption?
No. It is an encoding with no key, and anyone can decode it. A password or token in Base64 is as exposed as one in plain text.
What are the = signs at the end?
Padding. Base64 writes three bytes as four characters. If the input length is not a multiple of three, one or two = fill the last group. The decoder on this page also accepts Base64 with the padding left off.
What is URL-safe Base64?
A variant that replaces + with - and / with _, and usually drops the padding, so the result can sit in a URL or file name without escaping. The decoder accepts both alphabets.
Why does decoding say the bytes are not UTF-8 text?
The Base64 is valid, but what it contains is not text. It is probably a file such as an image, a PDF or compressed data. For images, use the Base64 to image tool.
How much bigger does Base64 make my data?
Four characters for every three bytes, so about 33% larger, plus up to two padding characters.

Sources

More in Encoding