What is Base64 encoding?

Base64 converts binary data into a string of 64 printable ASCII characters (A-Z, a-z, 0-9, +, /). It is used to safely transmit binary data over channels that only support text, such as email or JSON.

What is URL-safe Base64?

URL-safe Base64 replaces + with - and / with _ so the output can appear in URLs and file names without percent-encoding. It is defined in RFC 4648 Section 5.

How does this tool handle Unicode and emoji?

The tool uses the TextEncoder API to convert text to its UTF-8 byte sequence before encoding, so emoji and non-ASCII characters are handled correctly. Decoding reverses this with TextDecoder.

What happens if I decode an invalid Base64 string?

The tool catches the error and displays a clear error message explaining that the input is not valid Base64. Common causes include incorrect padding or characters outside the Base64 alphabet.

Is my data sent to a server?

No. All encoding and decoding runs entirely in your browser using JavaScript. Nothing is transmitted to any server.

What is the size overhead of Base64?

Base64 increases data size by approximately 33% because every 3 bytes of input produce 4 characters of output.

Base64 Encoder / Decoder

Name: Base64 Encoder / Decoder
Availability: InStock
Author: Nham Vu

Encode any text to Base64 or decode a Base64 string back to plain text — supports standard and URL-safe alphabets with full Unicode handling.

Encode

text → Base64

Input — plain text

Alphabet Standard URL-safe

Base64 output

Decode

Base64 → text

Input — Base64 string Decoded output

Copied!

Summary

Encode any text to Base64 or decode a Base64 string back to plain text — supports standard and URL-safe alphabets with full Unicode handling.

How it works

Select the Encode or Decode tab.
Paste your text or Base64 string into the input field.
Choose Standard or URL-safe alphabet.
The output updates instantly.
Click Copy to copy the result to your clipboard.
The output character count is displayed below the result.

Use cases

Encode binary data for embedding in JSON or XML payloads.
Decode Base64-encoded JWT payloads to inspect their claims.
Prepare Base64 strings for HTTP Basic Auth headers (user:pass).
Convert URL-safe Base64 tokens used in OAuth and PKCE flows.
Encode Unicode text (emoji, CJK characters) for safe transport.
Quickly verify that a Base64 string is valid before using it in code.
Generate data URIs for embedding small assets in HTML or CSS.
Inspect Base64-encoded cookies or session tokens.

Frequently Asked Questions

Last updated: 2026-06-09 · Reviewed by Nham Vu