Base64 Encode & Decode Online

How to Use the Base64 Encoder/Decoder

1. Choose your mode - Click "Encode" to convert text or files to Base64, or "Decode" to convert Base64 back to readable text.
2. Enter your data - Type or paste your text into the input field. You can also drag and drop a file onto the upload area when encoding.
3. Get results instantly - With live mode enabled, the output updates as you type. You can also click the action button manually.
4. Copy or swap - Use the "Copy Output" button to copy the result to your clipboard, or the "Swap" button to move the output back to the input for further processing.

Tips for Best Results

• Use UTF-8 encoding (the default) unless you have a specific reason to use another character set.
• When encoding files, the tool generates a complete data URI that you can use directly in HTML or CSS.
• When decoding image data, the tool automatically detects the image type and shows a preview.
• The "Split into lines" option adds line breaks every 76 characters, which is useful for MIME-compliant encoding (such as email).

What is Base64 Encoding?

Base64 is a binary-to-text encoding scheme that represents binary data using a set of 64 ASCII characters. It was designed to allow binary data to be transmitted over channels that only reliably support text content, such as email protocols and HTML documents.

The Base64 alphabet consists of uppercase letters (A-Z), lowercase letters (a-z), digits (0-9), and two additional characters (+ and /). The = character is used for padding when the input length is not divisible by 3.

How Base64 Works

The encoding process takes every 3 bytes (24 bits) of input data and splits them into four groups of 6 bits each. Each 6-bit group is then mapped to one of the 64 characters in the Base64 alphabet. This is why Base64-encoded data is approximately 33% larger than the original.

Original:    M        a        n
ASCII:       77       97       110
Binary:      01001101 01100001 01101110
6-bit groups: 010011 010110 000101 101110
Base64:       T      W        F      u

If the input data is not a multiple of 3 bytes, padding characters (=) are appended to the output to make the total length a multiple of 4.

Common Uses of Base64

• Email attachments - MIME encoding uses Base64 to embed binary attachments (images, documents) in email messages that only support 7-bit ASCII text.
• Data URIs - Embed images, fonts, and other resources directly in HTML or CSS files using data: URIs, eliminating extra HTTP requests.
• API communication - Many REST APIs use Base64 to encode binary data in JSON payloads, which only support text strings.
• HTTP Basic Authentication - Credentials are encoded as username:password in Base64 before being sent in the Authorization header.
• Storing binary data in text formats - Configuration files, XML documents, and databases that only accept text can store binary data as Base64 strings.
• Cryptographic operations - Keys, certificates, and encrypted data are often represented in Base64 for easy storage and transmission (PEM format, JWTs).

Base64 in Web Development

Data URIs in HTML and CSS

Data URIs allow you to embed resources directly in your code. This can reduce HTTP requests and improve page load performance for small assets like icons and simple graphics.

<!-- Embedding an image in HTML -->
<img src="data:image/png;base64,iVBORw0KGgo..." alt="icon">

/* Embedding a background image in CSS */
.icon {
  background-image: url('data:image/svg+xml;base64,PHN2Zy...');
}

While data URIs are convenient, they do increase the size of your HTML/CSS files by about 33%. They are best used for small assets under 5-10 KB. For larger files, separate HTTP requests with proper caching are more efficient.

HTTP Basic Authentication

When accessing a protected API endpoint using Basic Authentication, the credentials are Base64-encoded and included in the request header:

// JavaScript example
const credentials = btoa('username:password');
fetch('https://api.example.com/data', {
  headers: {
    'Authorization': 'Basic ' + credentials
  }
});

Note that Base64 encoding is not encryption. Basic Authentication should always be used over HTTPS to protect credentials in transit.

Email Encoding (MIME)

Email protocols were originally designed for 7-bit ASCII text. To send binary attachments, MIME uses Base64 encoding with lines split at 76 characters. The Content-Transfer-Encoding header indicates Base64 is used:

Content-Type: image/png; name="photo.png"
Content-Transfer-Encoding: base64

iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mNk
+M9QDwADhgGAWjR9awAAAABJRU5ErkJggg==

Frequently Asked Questions