Base64 Encode & Decode Online — What Is Base64 and How to Use It

You've probably seen strings like SGVsbG8gV29ybGQ= in API responses, email headers, or browser URLs. That's Base64. This guide explains what Base64 encoding is, why it exists, and how to encode and decode it instantly online.

What Is Base64?

Base64 is an encoding scheme that converts binary data into a string of 64 printable ASCII characters. The 64 characters are:

• Uppercase letters: A–Z (26)
• Lowercase letters: a–z (26)
• Digits: 0–9 (10)
• Two symbols: + and / (2)
• Padding character: =

The encoding works by taking every 3 bytes (24 bits) of input and splitting them into four 6-bit groups. Each 6-bit group maps to one of the 64 characters.

Why Is Base64 Used?

Some protocols (like email via SMTP, or certain HTTP headers) were designed to handle only text, not arbitrary binary data. Base64 solves this by representing any binary data as safe, printable text. Common use cases include:

1. Embedding images in HTML/CSS

Instead of referencing an image file, you can embed it directly using a Data URL:

<img src="data:image/png;base64,iVBORw0KGgo..." />

This reduces HTTP requests but increases file size. Use the Image to Base64 Converter for this.

2. API authentication

HTTP Basic Authentication encodes credentials as Base64:

Authorization: Basic dXNlcm5hbWU6cGFzc3dvcmQ=

Note: Base64 is not encryption. Anyone can decode it. Always use HTTPS.

3. Email attachments (MIME)

Email attachments are encoded in Base64 so binary files (PDFs, images) can travel through text-based email protocols.

4. JWT tokens

JSON Web Tokens use Base64URL (a URL-safe variant) to encode the header and payload. Use the JWT Decoder to inspect them.

5. Storing binary data in JSON or XML

Since JSON strings must be valid Unicode text, binary data (images, files) must be Base64-encoded before embedding.

Base64 Encoding Example

Let's encode the word "Hello":

Character	ASCII (decimal)	Binary (8-bit)
H	72	01001000
e	101	01100101
l	108	01101100
l	108	01101100
o	111	01101111

The 5 bytes (40 bits) are grouped into six 6-bit chunks, mapped to Base64 characters, and padded with = to make the output a multiple of 4: SGVsbG8=

How to Encode Base64 Online

1. Go to the QuickTools Base64 Tool
2. Select Encode mode
3. Type or paste your text
4. The Base64 output appears instantly
5. Click Copy

How to Decode Base64 Online

1. Go to the QuickTools Base64 Tool
2. Select Decode mode
3. Paste the Base64 string (e.g. SGVsbG8=)
4. The decoded text appears instantly

If the Base64 string decodes to binary (not readable text), the tool will indicate that the output is binary data.

Base64 vs Base64URL

Standard Base64 uses + and /, which have special meaning in URLs. Base64URL replaces them with - and _, making encoded strings safe to use in URLs and filenames without percent-encoding.

Variant	Special chars	Use case
Base64	+/=	Email, general encoding
Base64URL	-_ (no padding)	JWT, URLs, filenames

Base64 in JavaScript

// Encode
const encoded = btoa("Hello World");
// → "SGVsbG8gV29ybGQ="

// Decode
const decoded = atob("SGVsbG8gV29ybGQ=");
// → "Hello World"

Note: btoa() only works with Latin-1 characters. For Unicode strings, encode to UTF-8 bytes first.

Base64 in Python

import base64

# Encode
encoded = base64.b64encode(b"Hello World").decode()
# → 'SGVsbG8gV29ybGQ='

# Decode
decoded = base64.b64decode("SGVsbG8gV29ybGQ=").decode()
# → 'Hello World'