Free Base64 Decoder
New PopularFree online Base64 decoder. Convert Base64 strings back to readable text, preview encoded images, detect file types, decode JWT tokens with expiration status, and download decoded files. Handles standard and URL-safe Base64 automatically.
How to Use
Paste any Base64-encoded text, data URI, or JWT token into the input field. The tool automatically detects the type and switches to the best view.
The tool decodes instantly. For images, see a live preview. For JWT tokens, see decoded header, payload, and expiration status. For files, download with one click.
Use the JWT Decoder tab to inspect API tokens and check expiration. Use the Batch tab to decode multiple Base64 strings at once. Both standard and URL-safe Base64 are handled automatically.
Copy the decoded text, download decoded files and images, or use the Swap button to move the decoded output back into the input for re-encoding with different settings.
What Does Base64 Decoding Do?
Base64 decoding is the reverse of encoding — it converts a Base64-encoded ASCII string back to its original binary or text form. This is necessary whenever you receive Base64-encoded data from an API, email attachment, JWT token, data URI, or configuration file and need to inspect or use the original content.
Common Decoding Scenarios
- API responses — Many APIs return binary data (images, certificates, files) encoded as Base64 inside JSON fields. Paste the value here to inspect or download the original content.
- JWT token inspection — JSON Web Tokens encode their header and payload in Base64URL format. The JWT Decoder tab automatically splits the token, decodes each part, and shows the expiration time and status.
- Data URI extraction — Paste a
data:image/png;base64,...URI to see the image preview and download the original file. - Email attachments — MIME-encoded email attachments are Base64 text blocks in the raw email source. Decode them to retrieve the original file.
- Encoded configuration values — Kubernetes secrets, environment variables, and some CI/CD systems store values as Base64. Decode them to read the actual configuration.
Intelligent Auto-Detection
When you paste content, this decoder automatically detects what it is: a JWT token (auto-switches to JWT Decoder), a data URI (auto-switches to Image Preview), standard Base64, or plain text. The decoded content type is also detected — JSON is identified for easy reading, images show a live preview, and binary files offer a download button.
Privacy
All decoding happens entirely in your browser using JavaScript. Your Base64 strings, JWT tokens, and files never leave your device — nothing is sent to any server, stored, or logged.
Frequently Asked Questions
Paste your Base64-encoded string into the input field with "Decode" direction selected. The tool decodes instantly and shows the result. It automatically detects whether the decoded content is plain text, JSON, an image, or a binary file.
Yes. Paste a JWT token (three dot-separated segments) and the tool automatically detects it and switches to JWT Decoder mode. It decodes the header (algorithm), payload (user data and claims), and shows the expiration status — whether the token is still valid or already expired, and by how much.
This usually means the original content was a binary file (image, PDF, ZIP, executable) rather than text. The tool detects binary content and suggests downloading it rather than displaying it as text. Try the Image tab (if you suspect it is an image) or paste the decoded content into the File mode area.
Yes. Paste the complete data URI (e.g., data:image/png;base64,iVBOR…) and the tool extracts the Base64 content, decodes it, and shows a preview if it is an image, or offers a download for other file types. The Image tab's decode mode is optimized specifically for this.
Standard Base64 uses +, /, and = characters. Base64URL (used in JWTs and URL parameters) replaces + with -, / with _, and typically omits padding =. This decoder handles both formats automatically — you do not need to specify which one or convert between them manually.
Yes. Switch to the Batch tab, set direction to Decode, and enter one Base64 string per line. The tool decodes each one separately and shows results aligned line by line. Failed decodings are clearly marked with an error message for that specific line.
Common causes: extra spaces or newlines (the tool auto-strips these), invalid characters that are not part of the Base64 alphabet, incorrect padding (missing = at the end), or a string that is not actually Base64-encoded. Check that you copied the complete Base64 string without truncation.