How do I decode a Base64 string?

Paste your Base64 string into the input box and click Decode. The tool auto-detects whether it is standard or URL-safe Base64 and converts it back to the original text. You can also select the mode manually.

How do I tell if a Base64 string is standard or URL-safe?

Standard Base64 uses + and / characters and ends with = padding. URL-safe Base64 uses - and _ instead of + and / and typically has no = padding. JWT tokens always use URL-safe Base64. The Auto-detect mode in this tool handles both automatically.

Can I use this tool to decode JWT token payloads?

Yes. A JWT has three parts separated by dots (header.payload.signature). Each part is URL-safe Base64-encoded. Copy the middle section (payload) and decode it in URL-safe mode to see the JSON claims.

What happens when I try to decode invalid Base64?

Invalid Base64 input produces an error message. Common causes include stray whitespace inside the string (outside the boundaries), characters not in the Base64 alphabet, or incorrect padding. The tool shows a red error state with details.

What is Base64 padding and why might it be missing?

Base64 output must have a length that is a multiple of 4. When the input is not a multiple of 3 bytes, = characters are appended as padding. URL-safe Base64 (used in JWT) often omits padding. This tool automatically adds missing padding before decoding.

Can I decode binary files from Base64?

You can decode the Base64 and download the result as a .txt file. For binary files like images or PDFs, use the Base64 Image Converter tool which handles MIME types and produces the correct file format.

What are the security risks of Base64-encoded data?

Base64 provides no security — it is trivially reversible. Sensitive data like passwords, API keys, or PII should never be stored or transmitted as Base64 alone. Always use proper encryption (AES, TLS) for sensitive information.

Is my data sent to any server when I use this tool?

No. All decoding runs entirely in your browser via JavaScript. No data is transmitted to any server, making it safe for sensitive Base64 strings like JWT tokens or API credentials.

Base64
Decoder

Base64를 텍스트로 디코딩

디코딩 방식:

Auto-detect

Standard

URL-safe

Base64 문자열을 입력하거나 붙여넣으세요

입력 (Base64) 0자

출력 (디코딩된 텍스트) 복사

Base64Decoder

Base64
Decoder