Base64 Encoder/Decoder

Free Base64 encoder and decoder. Encode plain text or UTF-8 strings to Base64, or decode Base64 back to readable text instantly in your browser.

More free online encoding tools — no install required.

What Base64 Encoder/Decoder Does

It encodes a UTF-8 string into a Base64-encoded ASCII string, or decodes a Base64 string back into its original UTF-8 text. It also validates whether a given string is structurally valid Base64 before attempting decoding.

Who Uses This Tool

Base64 Encoder/Decoder is built for Web developers, backend engineers, API integrators, security researchers, QA testers, DevOps engineers. Whether you are processing data as part of an automated pipeline or need a quick one-off conversion in your browser, the tool requires no installation and no account — paste your input and get your result in seconds.

Primary Use Case

Encoding an authorization credential (e.g. username:password) into Base64 for use in an HTTP Basic Auth header.

The Problem It Solves

Binary and non-ASCII data breaks in plain-text contexts like email, JSON payloads, and HTML attributes. Base64 encoding makes any string safe to transmit or embed in text-only systems — and this tool removes the need to write that conversion manually.

Example

Input
Hello, World!
Output
SGVsbG8sIFdvcmxkIQ==

When to Use This Tool

Use this tool when encoding API payloads, debugging tokens, working with binary-safe transport formats, handling data URIs, or decoding Base64 responses during development and security analysis.

What to Do With the Output

They paste the encoded string directly into API headers, config files, HTML data attributes, JWT payloads, or email MIME fields — or they decode a received Base64 string to inspect its raw content during debugging.

Common Mistakes to Avoid

Treating Base64 as encryption — it provides zero security and is trivially reversible Pasting URL-safe Base64 with - and _ instead of standard + and / characters, which causes a validation error Including whitespace or line breaks in the input — strip them before decoding Forgetting that = padding is required — a string whose length is not a multiple of 4 will fail validation Trying to decode plain text that was never Base64-encoded in the first place

How It Works

The tool converts UTF-8 text into Base64 using browser-safe encoding logic and decodes Base64 back into readable Unicode text. Validation logic detects malformed Base64 structures, invalid characters, and corrupted padding sequences.

Pro Tip

Use the validate function before decoding an untrusted Base64 string. It checks length divisibility by 4, character set validity, and padding position — catching malformed strings that would silently fail or produce corrupted output in code.

Also Known As

Base64 Encoder/Decoder is also commonly referred to as base64 encode, base64 decode, b64 encoder, b64 decode, base-64 converter, encode to base64, decode from base64, base64 string converter, base64 online, atob btoa online. All of these terms describe the same conversion — no matter what you call it, this tool handles it.

Frequently Asked Questions

Base64 is used to represent binary or non-ASCII data as a plain ASCII string so it can safely travel through text-only systems — such as email, HTTP headers, JSON fields, or HTML attributes.
No. Base64 is encoding, not encryption. Any Base64 string can be decoded instantly without a key. Never use it to secure sensitive data.
Padding characters (=) are added when the input byte length isn't divisible by 3. Two = means one byte of padding was needed; one = means two bytes were needed. A string with no = had an input length perfectly divisible by 3.
Standard Base64 uses + and /. URL-safe Base64 replaces these with - and _. If your string came from a URL or JWT, replace - with + and _ with / before decoding.
Yes. The tool uses a UTF-8–safe encode path (encodeURIComponent + btoa) that correctly handles multi-byte characters, accented letters, and emoji that plain btoa() alone would reject.
It verifies that the string is non-empty, has a length divisible by 4, contains only valid Base64 characters (A–Z, a–z, 0–9, +, /, =), and that padding characters appear only at the end.
Base64 output is approximately 33% larger than the input — every 3 bytes of input produces 4 characters of output.