What is URL-safe Base64 decoding?

URL-safe Base64 uses different characters (- and _ instead of + and /) to avoid issues when the encoded string is used in URLs. Our decoder automatically detects and handles both standard and URL-safe Base64.

100% Client-Side Processing

Base64 Decode

Decode Base64 encoded strings instantly in your browser. Convert Base64 back to plain text, binary data, or files with our free, privacy-first decoder tool.

Base64 Decoder

URL-Safe Mode

BASE64 INPUT

0 characters

DECODED OUTPUT

0 characters

Switch to Encode

How to Use the Base64 Decoder

1 Paste your Base64 string - Enter the encoded text in the input field on the left.
2 Enable URL-Safe mode if needed - Check the box if your string uses URL-safe Base64 encoding (- and _ instead of + and /).
3 Click "Decode Base64" - The decoded result appears instantly in the output field.
4 Copy the result - Click the Copy button to copy the decoded text to your clipboard.

Common Use Cases

Email Attachments

Decode Base64 encoded email attachments and inline images from MIME messages.

API Responses

Decode Base64 data received from REST APIs, webhooks, or third-party services.

Authentication Tokens

Decode JWT payloads, API keys, and authentication credentials for debugging.

Data URIs

Extract embedded images, fonts, or files from data URIs in HTML/CSS.

Base64 Decode Examples

Example 1: Simple Text

Base64 Input: SGVsbG8gV29ybGQh

Decoded Output: Hello World!

Example 2: JSON Data

Base64 Input: eyJuYW1lIjoiSm9obiIsImFnZSI6MzB9

Decoded Output: {"name":"John","age":30}

Example 3: URL-Safe Base64

URL-Safe Base64 Input: PDw_Pz4-

Decoded Output: <<??>>

Frequently Asked Questions

What is Base64 decoding?

Base64 decoding is the reverse process of Base64 encoding. It converts Base64 encoded data back to its original binary or text format. Base64 is commonly used to encode binary data for transmission over text-based protocols.

Is my data safe when using this decoder?

Yes, completely safe! This Base64 decoder runs entirely in your browser using JavaScript. Your data never leaves your device and is never sent to any server. You can even use this tool offline once the page is loaded.

What is URL-safe Base64?

URL-safe Base64 replaces the + and / characters with - and _ respectively, making the encoded string safe to use in URLs without additional encoding. Enable the URL-Safe mode if your Base64 string uses these alternative characters.

Why is my Base64 decoding failing?

Common reasons include: invalid Base64 characters in the input, incorrect or missing padding (= characters at the end), whitespace or line breaks that need to be removed, or the string being double-encoded. Try removing any extra whitespace and ensure the string only contains valid Base64 characters.

Can I decode Base64 images?

Yes! This decoder can handle Base64 encoded images. For best results with images, use our full Base64 Encoder/Decoder tool which includes file support and image preview features.

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Technical Details

Base64 encoding uses a set of 64 characters (A-Z, a-z, 0-9, +, /) to represent binary data in an ASCII string format. The decoding process reverses this:

Character set: Standard Base64 uses A-Za-z0-9+/ with = for padding
URL-safe variant: Uses - instead of + and _ instead of /
Padding: The = character pads the output to be a multiple of 4 characters
Output ratio: Every 4 Base64 characters decode to 3 bytes of data

This decoder uses the native JavaScript atob() function with additional handling for URL-safe variants and Unicode characters via decodeURIComponent().