Base64 · Guide

What is Base64 Encoding?

5 min readUpdated January 2025Developer Tools

Base64 is everywhere in web development — in JWTs, data URLs, API authentication, and email attachments. But what exactly is it, why do we need it, and how do you use it?

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What is Base64?

Base64 is an encoding scheme that converts binary data into a string of ASCII characters. It uses a set of 64 characters — A-Z, a-z, 0-9, +, and / — to represent any sequence of bytes.

The name "Base64" refers to the 64 characters used in the encoding. Each Base64 character represents 6 bits of data, so 3 bytes (24 bits) of input become 4 Base64 characters (24 bits).

Example

Original text:  Hello, World!
Base64 encoded: SGVsbG8sIFdvcmxkIQ==

Why is Base64 used?

Binary data can contain bytes that have special meaning in certain contexts — for example, null bytes or line breaks that would break an email protocol or a URL. Base64 solves this by converting any binary data into safe, printable ASCII characters that can be transmitted through any text-based system.

Common use cases:

JWTs — the header and payload are Base64URL-encoded
Data URLs — embedding images directly in HTML/CSS (data:image/png;base64,...)
HTTP Basic Auth — credentials are sent as username:password Base64-encoded
Email attachments — MIME encoding for binary file attachments
API keys and tokens — many tokens are Base64-encoded for safe transmission
Cryptographic signatures — public keys and certificates use Base64 (PEM format)

Note: Base64 is encoding, not encryption. Anyone can decode a Base64 string — it provides no security. Never use Base64 to hide sensitive data.

Base64 vs Base64URL

Standard Base64 uses + and / characters, which have special meaning in URLs. Base64URL is a URL-safe variant that replaces + with - and / with _. JWTs use Base64URL encoding.

Variant	Characters used	Padding	Use case
Base64	A-Z, a-z, 0-9, +, /	= padding	General encoding, email
Base64URL	A-Z, a-z, 0-9, -, _	No padding	JWTs, URLs, filenames

How to encode and decode Base64 online

Open the Base64 encoder/decoder on tinybench.dev
Choose Encode or Decode mode
Paste your text or upload a file
Copy the result — all in your browser, nothing sent to a server

Base64 in code

JavaScript — browser

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

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

Python

import base64

# Encode
encoded = base64.b64encode(b'Hello, World!').decode('utf-8')

# Decode
decoded = base64.b64decode('SGVsbG8sIFdvcmxkIQ==').decode('utf-8')

Node.js

// Encode
const encoded = Buffer.from('Hello, World!').toString('base64');

// Decode
const decoded = Buffer.from('SGVsbG8sIFdvcmxkIQ==', 'base64').toString('utf-8');

Frequently asked questions

Does Base64 increase file size?

Yes. Base64 encoding increases the size of data by approximately 33%. For every 3 bytes of input, you get 4 bytes of Base64 output. This is a trade-off for compatibility with text-based systems.

What is the = padding at the end?

Base64 encodes 3 bytes at a time. If the input length isn't a multiple of 3, = padding characters are added to make the output length a multiple of 4. One = means 2 bytes remained; == means 1 byte remained.

Is Base64 the same as encryption?

No. Base64 is a reversible encoding anyone can decode without a key. Encryption scrambles data so only someone with the correct key can read it. Never use Base64 as a security measure.

Can I use Base64 for images in HTML?

Yes — using data URLs: <img src="data:image/png;base64,iVBOR...">. This embeds the image directly in HTML, eliminating an HTTP request. The trade-off is a larger HTML file and no browser caching of the image separately.

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