Base64 Decoder
Decode Base64 strings back to text online
Input
Options
URL-safe mode replaces + with - and / with _ for safe use in URLs.
Output
About This Tool
Base64 decoding is the everyday counterpart to encoding: you receive a Base64 string — a JWT payload, an HTTP Basic Auth header, a data URI, an email attachment part — and you need to see what's actually inside it. This tool decodes standard and URL-safe Base64 (handling - and _ in place of + and /) back to readable text instantly, entirely in your browser. It flags invalid Base64 input right away — stray characters, incorrect padding, truncated strings — so you know immediately whether what you pasted is genuinely Base64 or just looks like it.
How to Use
Paste the Base64 string you want to decode into the input field. The decoded text appears immediately in the output. If your Base64 came from a URL, query parameter, or filename, toggle 'URL-safe mode' so - and _ are interpreted correctly. If decoding fails, the tool shows exactly why (invalid character, incorrect length) rather than a blank result. Use 'Decode per line' when you have multiple separate Base64 strings, one per line.
Common Use Cases
JWT Inspection
Paste a JWT header or payload segment to see the underlying JSON claims without verifying the signature.
HTTP Basic Auth
Decode an Authorization header value like `Basic dXNlcm5hbWU6cGFzc3dvcmQ=` to recover the username:password pair.
Data URI Inspection
Decode the Base64 portion of a data: URI to inspect embedded image or font data.
Email Attachment Debugging
Decode a Base64 MIME part from raw email source to verify attachment content.
API Response Debugging
Decode a Base64 field returned by an API to check what data it actually contains.
Limitations & Important Notes
Base64 is encoding, not encryption — decoding recovers the exact original data, so never decode untrusted secrets on a shared or public machine. Decoding genuinely binary data (images, PDFs) works, but the raw output textarea may show unprintable characters — use a file-aware tool if you need to reconstruct a binary file. Invalid padding or stray whitespace causes a decode error rather than a silent repair. For very large Base64 payloads, browser memory limits may apply — use a command-line tool like `base64 -d` for large-scale batch decoding.