About Base64 Decode

Decode Base64 back to text or file. Part of the DevTools Surf developer suite. Browse more tools in the Encoding collection.

Use Cases

• Decoding Base64-encoded email attachments for inspection
• Reading encoded JWT payloads without a full JWT decoder
• Extracting binary files embedded as Base64 in JSON responses
• Debugging data URIs containing Base64-encoded images

Tips

• Decode Base64 strings from API responses to read payloads
• Detect whether the output is text or binary file content
• Handle URL-safe Base64 variants with - and _ characters

Fun Facts

• Base64 encoding was first defined in RFC 1421 in 1993 for Privacy Enhanced Mail (PEM), predating its use on the web.
• Base64 increases data size by approximately 33% because it encodes 3 bytes of binary into 4 ASCII characters.
• The 64-character alphabet uses A-Z, a-z, 0-9, + and /, chosen because they are all printable in every character encoding.

FAQ

Which Base64 variants are supported?

Standard (with +/=) and URL-safe (with -_). The tool auto-detects from input characters.

What if decoding fails?

Clear error with the position of invalid characters. Common causes: missing padding (=), extra whitespace, or mixing standard and URL-safe alphabets.

Can it handle binary output?

Yes — decode to download. Useful for extracting files from data URIs or Base64-encoded binary blobs.

What about Base64-in-Base64 (double encoding)?

Decode once, then feed the result back. Each pass removes one layer. Common in scenarios where a Base64 string is embedded in another Base64 payload.