Base64 Encode & Decode Online — Free Tool & Developer Guide (2026)

Base64 is a binary-to-text encoding scheme that converts any data into a string of 64 printable characters. It lets you safely pass binary content — files, credentials, tokens — through systems that only understand plain text. Encoding a string takes one second; the free Base64 Converter does it entirely in your browser.

This guide explains how Base64 works, where developers actually use it, how to encode and decode strings without installing anything, and the one mistake that catches beginners — confusing encoding with encryption.

What is Base64 encoding?

Base64 takes any input — text, a binary file, an image — and maps every 3 bytes of raw data to exactly 4 printable ASCII characters drawn from an alphabet of 64: uppercase A–Z, lowercase a–z, digits 0–9, plus + and /.

A quick example — encoding the word Hello:

The trailing = and == are padding. Because Base64 works in 3-byte groups, if the input length is not a multiple of 3, padding characters fill the final group. One = means one byte of padding; two means two. This is expected and correct — not an error.

The output is always about 33% larger than the input — the cost of representing binary data as printable text.

Why developers use Base64

Base64 solves a specific problem: many protocols and formats — HTTP headers, JSON, XML, email — were designed to carry text only. When you need to include binary content in those channels, Base64 converts it to a text-safe representation without corrupting the data.

How to encode and decode Base64 online

The NextUtils Base64 Converter handles text strings, files, and images entirely in your browser. Nothing is sent to a server:

Base64 encode and decode in code

Every major language has native Base64 support. Here are the one-liners you will use most often:

JavaScript (browser)

// Encode
btoa("Hello, World!")         // → "SGVsbG8sIFdvcmxkIQ=="

// Decode
atob("SGVsbG8sIFdvcmxkIQ==") // → "Hello, World!"

// Encode with Unicode support (btoa fails on non-ASCII)
btoa(encodeURIComponent("café")) // → encode first, then btoa

JavaScript (Node.js)

// Encode
Buffer.from("Hello, World!").toString("base64")
// → "SGVsbG8sIFdvcmxkIQ=="

// Decode
Buffer.from("SGVsbG8sIFdvcmxkIQ==", "base64").toString("utf8")
// → "Hello, World!"

// Build a Basic Auth header
const token = Buffer.from("user:pass").toString("base64");
fetch(url, { headers: { Authorization: `Basic ${token}` } });

Python

import base64

# Encode
base64.b64encode(b"Hello, World!").decode()
# → 'SGVsbG8sIFdvcmxkIQ=='

# Decode
base64.b64decode("SGVsbG8sIFdvcmxkIQ==").decode()
# → 'Hello, World!'

# URL-safe variant (for JWT, URL params)
base64.urlsafe_b64encode(b"Hello")

Bash / terminal

# Encode
echo -n "Hello, World!" | base64
# → SGVsbG8sIFdvcmxkIQ==

# Decode
echo "SGVsbG8sIFdvcmxkIQ==" | base64 --decode
# → Hello, World!

# Build an Authorization header
echo -n "user:password" | base64

Why use a browser-based Base64 tool?

Credentials and tokens encoded as Base64 are common — and pasting them into a server-side tool means those values travel over a network. A browser-based tool removes that risk entirely:

Standard Base64 vs Base64url

There are two common variants. Knowing which to use prevents a subtle class of bug:

If you are decoding a JWT and getting garbled output, switch to a Base64url decoder (or replace - with + and _ with / before decoding). Use the JWT Decoder for JWT-specific decoding — it handles Base64url automatically.

Related developer tools

Frequently asked questions