Free Base64 Decoder Online | Decode Text, Files & Binary Data Instantly

Base64 Decoder

Input

Character set:Show alternative namesEncode line by lineNewline separator:

Output

⭐ Why Choose Our Base64 Decoder

👁️ Real-time decoding preview with validation
📁Support for large files (up to 10MB)
🔒100% client-side processing (no server upload)
📋One-click copy/download decoded results
📱Mobile-optimized responsive interface
📊Detailed decoding examples with explanations
🔍Automatic file type detection

🔧 How Base64 Decoding Works: Step-by-Step Guide for base64-decoder

Input Validation

🔍 Verify the Base64 string follows RFC 4648 standards

Character Mapping

📊 Convert each Base64 character to its 6-bit value

Bit Regrouping

🧩 Combine four 6-bit chunks into 24-bit sequences

Original Data Reconstruction

💾 Split into original 8-bit bytes and convert to output format

⚙ ️ Technical Specifications

🔡Character Set

Accepts RFC 4648 standard Base64 alphabet plus variants:

Type	Characters	Notes
0 -25	A-Z	🔠 Uppercase letters
2 6-51	a-z	🔡 Lowercase letters
5 2-61	0 -9	🔢 Digits
6 2-63	+/	⚡ Standard symbols
	=	⏹ ️ Padding character
	-_	🌐 URL-safe variant

📈Efficiency Metrics

Decoding size comparison:

Base64 Size	Original Size	Reduction
4 characters	3 bytes	🔽 25%
1 .33KB	1 KB	🔽 25%
1 .33MB	1 MB	🔽 25%

⏱️ Performance Benchmarks

Average processing times (Chrome v120):

File Size	Decoding Time
1 KB	⚡ <50ms
1 00KB	⚡ <300ms
1 MB	⏳ <1.5s
1 0MB	⏳ <8s

💻 Command Line Alternatives

Native Base64 tools across platforms:

🐧Linux/macOS

🔤Decode string

echo 'SGVsbG8=' | base64 --decode

Basic string decoding

📁Decode file

base64 -d input.b64 > output.txt

Base64 to file conversion

🪟Windows

🔌PowerShell decode

[Text.Encoding]::UTF8.GetString([Convert]::FromBase64String("SGVsbG8="))

Native PowerShell method

⌨️ CMD decode

certutil -decode input.b64 output.txt

Built-in Windows utility

🛠 ️ Practical Applications

🌐Web Development

🖼️ Extract images from Data URIs
⚡Decode API responses
💾Parse LocalStorage data

const binaryString = atob('iVBORw0KGgo...');

const decodedData = JSON.parse(atob(localStorage.getItem('cache')));

📧Email Processing

📎Decode email attachments
📨Process MIME messages
🔍Analyze EML files

Content-Transfer-Encoding: base64

const attachment = Buffer.from(encodedContent, 'base64');

❓ Frequently Asked Questions

❓ Why does my decoded output look corrupted?

Usually indicates: 1) Invalid Base64 characters, 2) Missing padding '=', or 3) The data was originally binary (try saving as file rather than viewing as text).

🔗 How to handle URL-safe Base64?

Replace '-' with '+' and '_' with '/', then add padding '=' as needed before decoding. This converts web-safe Base64 back to standard format.

🔒 Is Base64 decoded data secure?

Base64 is not encryption - it's encoding. For sensitive data, ensure proper encryption (like AES) was used before the original encoding.

📏 What's the maximum file size for decoding?

Our web tool handles files up to 10MB efficiently. For optimal performance, we recommend files under 2MB. Larger files should use command-line tools.

Pro Tips

💡Best Practice

For debugging, first validate your Base64 string with our tool before attempting to decode it in your application.

🔍Best Practice

Always check the output size after decoding - it should be ~25% smaller than the Base64 input.

⚡Best Practice

Combine with gzip decompression when handling large decoded data that was previously compressed.