Base64 Encoder & Decoder

What is Base64 Encoding?

Base64 is a binary-to-text encoding scheme defined in RFC 4648. It represents binary data using a set of 64 ASCII characters: A-Z, a-z, 0-9, +, and /, with = used for padding. Base64 is one of the most widely used encoding formats on the web, found in emails, data URIs, APIs, and configuration files.

The primary purpose of Base64 is to allow binary data to be safely transmitted through text-based systems that may not handle raw binary correctly — such as email (MIME), JSON payloads, HTML attributes, and URL parameters.

How Base64 Encoding Works

Base64 encoding works by dividing the input data into groups of 3 bytes (24 bits). Each group is then split into four 6-bit values, and each 6-bit value is mapped to one of the 64 characters in the Base64 alphabet. If the input length is not a multiple of 3, the output is padded with one or two = characters.

Step-by-Step Example: Encoding "Man"

Here is how the string Man is converted to its Base64 representation TWFu:

Step	M	a	n
ASCII value	77	97	110
Binary (8 bits)	01001101	01100001	01101110

The 24 bits (010011010110000101101110) are regrouped into four 6-bit values:

6-bit group	010011	010110	000101	101110
Decimal value	19	22	5	46
Base64 character	T	W	F	u

Result: Man → TWFu. When the input length is not a multiple of 3, padding (=) is added: Ma → TWE= and M → TQ==.

The Base64 Character Set

Value	Char	Value	Char	Value	Char	Value	Char
0	A	16	Q	32	g	48	w
1	B	17	R	33	h	49	x
2	C	18	S	34	i	50	y
3	D	19	T	35	j	51	z
4	E	20	U	36	k	52	0
5	F	21	V	37	l	53	1
6	G	22	W	38	m	54	2
7	H	23	X	39	n	55	3
8	I	24	Y	40	o	56	4
9	J	25	Z	41	p	57	5
10	K	26	a	42	q	58	6
11	L	27	b	43	r	59	7
12	M	28	c	44	s	60	8
13	N	29	d	45	t	61	9
14	O	30	e	46	u	62	+
15	P	31	f	47	v	63	/

Base64URL Variant

The Base64URL encoding (also defined in RFC 4648, Section 5) is a URL-safe variant that replaces + with - and / with _. It also typically omits the = padding characters. Base64URL is safe for use in URLs and filenames without percent-encoding.

Base64URL is used in JSON Web Tokens (JWT), URL parameters, and filenames where standard Base64 characters would need to be percent-encoded. If you are working with JWT tokens, try our JWT Decoder & Encoder tool.

Common Uses of Base64

• Data URIs: Embedding images, fonts, or other assets directly in HTML or CSS using data:[type];base64,[data].
• Email attachments: MIME encoding uses Base64 to embed binary attachments in email messages. Use the "Line wrap (76 chars, MIME)" option above for MIME-compliant output.
• API payloads: Transmitting binary data (images, documents, certificates) in JSON or XML APIs.
• Authentication: HTTP Basic Authentication encodes username:password in Base64.
• JSON Web Tokens: JWT header and payload are Base64URL-encoded.
• Certificates and keys: PEM-formatted certificates and SSH keys use Base64 encoding.
• Source maps: Inline source maps in JavaScript and CSS use Base64-encoded data URIs.

Base64 in Programming Languages

JavaScript

JavaScript provides built-in btoa() and atob() functions for Base64 encoding and decoding. For UTF-8 strings, use TextEncoder and TextDecoder to handle multi-byte characters correctly.

// Encode
const encoded = btoa('Hello, World!');  // "SGVsbG8sIFdvcmxkIQ=="

// Decode
const decoded = atob('SGVsbG8sIFdvcmxkIQ==');  // "Hello, World!"

// UTF-8 safe encode (handles emoji, CJK, etc.)
const utf8Encode = btoa(String.fromCharCode(
  ...new TextEncoder().encode('Hello ')
));

// UTF-8 safe decode
const bytes = Uint8Array.from(atob(encoded), c => c.charCodeAt(0));
const utf8Decode = new TextDecoder().decode(bytes);

Python

Python's base64 module provides b64encode() and b64decode(), plus urlsafe_b64encode() for URL-safe Base64.

import base64

# Encode
encoded = base64.b64encode(b'Hello, World!')  # b'SGVsbG8sIFdvcmxkIQ=='

# Decode
decoded = base64.b64decode(b'SGVsbG8sIFdvcmxkIQ==')  # b'Hello, World!'

# URL-safe variant (replaces + with - and / with _)
url_safe = base64.urlsafe_b64encode(b'Hello, World!')

# Encode a string (must encode to bytes first)
text = 'Hello'
encoded_str = base64.b64encode(text.encode('utf-8')).decode('ascii')

Java

Java 8+ provides java.util.Base64 with getEncoder(), getDecoder(), getUrlEncoder(), and getMimeEncoder().

import java.util.Base64;
import java.nio.charset.StandardCharsets;

// Encode
String encoded = Base64.getEncoder()
    .encodeToString("Hello, World!".getBytes(StandardCharsets.UTF_8));
// "SGVsbG8sIFdvcmxkIQ=="

// Decode
byte[] decoded = Base64.getDecoder().decode("SGVsbG8sIFdvcmxkIQ==");
String text = new String(decoded, StandardCharsets.UTF_8);

// URL-safe encoding
String urlSafe = Base64.getUrlEncoder().withoutPadding()
    .encodeToString("Hello, World!".getBytes(StandardCharsets.UTF_8));

// MIME encoding (76-char line wrap)
String mime = Base64.getMimeEncoder()
    .encodeToString(largeByteArray);

PHP

PHP provides base64_encode() and base64_decode() as built-in functions.

// Encode
$encoded = base64_encode('Hello, World!');  // "SGVsbG8sIFdvcmxkIQ=="

// Decode
$decoded = base64_decode('SGVsbG8sIFdvcmxkIQ==');  // "Hello, World!"

// Strict mode (returns false on invalid characters)
$result = base64_decode($input, true);
if ($result === false) {
    echo "Invalid Base64 input";
}

// Encode a file
$fileData = file_get_contents('image.png');
$base64File = base64_encode($fileData);

Character Encoding Support

This tool supports 29 character encodings for Base64 encoding and decoding, allowing you to work with text in virtually any Western, Cyrillic, Greek, Arabic, Hebrew, Thai, or Vietnamese script. Select the appropriate encoding from the dropdown to ensure your text is correctly converted to and from Base64.

Supported encoding families include UTF-8, ASCII, ISO-8859 (Latin-1 through Latin-10), Windows code pages (1250–1258, 874), KOI8-R, KOI8-U, IBM-866, and Macintosh Roman. All encoding and decoding is performed entirely in your browser — no data is sent to any server.

Base64 vs Encryption

Base64 is not encryption. It is a reversible encoding that provides no security whatsoever. Anyone can decode Base64 data without any key or password. Base64 is designed for data transport and compatibility, not for data protection. If you need to protect sensitive data, use actual encryption algorithms like AES or RSA.

Frequently Asked Questions