Base64 Encoding Explained

What Is Base64?

Base64 is an encoding scheme that converts binary data into a string of 64 printable ASCII characters. It was designed to safely transport data through systems that only handle text — like email protocols or URL parameters.

It is not encryption. Base64 is fully reversible without any key. Anyone who sees a Base64 string can decode it instantly.

How It Works

Every 3 bytes of input (24 bits) become 4 Base64 characters (6 bits each). The 64 characters used are:

A–Z  (26 characters)
a–z  (26 characters)
0–9  (10 characters)
+  /  ( 2 characters)
=    (padding)

Example:

Input:   Hello
Binary:  01001000 01100101 01101100 01101100 01101111
Base64:  SGVsbG8=

The = at the end is padding to make the output length a multiple of 4.

When to Use Base64

Use case	Why Base64 helps
Embedding images in HTML/CSS	<img src="data:image/png;base64,..."> avoids extra HTTP requests
JSON payloads with binary data	JSON is text-only; Base64 wraps binary safely
Basic Auth headers	Credentials are Base64-encoded in Authorization: Basic ...
Data URIs	Inline fonts, SVGs, or small files in stylesheets
JWT tokens	The header and payload parts are Base64url-encoded

Base64 vs Base64url

Standard Base64 uses + and /, which are special characters in URLs. Base64url replaces them with - and _ and omits padding — safe to use directly in URLs and JWT tokens without percent-encoding.

Common Pitfalls

1. Treating it as encryption
Base64 provides zero security. Never use it to "hide" sensitive data.

2. Expecting smaller output
Base64 output is ~33% larger than the input. Encoding a 1 MB image produces ~1.35 MB of text.

3. Double-encoding
If you encode an already-Base64 string, you get garbage. Decode first, then re-encode if needed.

4. Forgetting padding
Some libraries drop the = padding. If decoding fails, try appending = characters until the length is a multiple of 4.

Try It Now

Use the Base64 Encoder / Decoder to encode or decode any string instantly in your browser — nothing is sent to a server.

For URL-safe encoding of query parameters, the URL Encoder handles percent-encoding which is often a better fit than Base64 in that context.