About this tool
Paste complete Base64 to check its characters, length, and padding before restoring the bytes. MIME types can come from Data URIs, while file signatures provide format clues. You can customize the download name.
How to use
- Paste raw Base64 or a Base64 Data URI beginning with data:.
- Set the filename, extension, and MIME type if needed.
- Decode the input, then review the file size, detected type, and any messages.
- Download the file. It will not open or run automatically.
Features
- Accepts raw Base64 and Data URIs with MIME labels.
- Allows valid whitespace and line breaks while checking characters, length, and padding.
- Checks decoded bytes for file signatures and suggests a download extension.
- Lets you change the filename and MIME type without altering the restored bytes.
Decoding and file types
- If no MIME type is available, application/octet-stream is used as a fallback. File signature detection can provide a format reference.
- Unknown formats default to decoded-file.bin. Recognized formats such as PDF or PNG can use the corresponding extension.
- A Data URI's type label and the filename do not guarantee that the contents match. Check the detection result.
- Decoded HTML, SVG, or scripts are offered only as downloadable files and are not automatically rendered on this page.
Limits
- The decoded file must be no larger than 20 MiB. Input text length is also limited. Avoid pasting text far beyond the limit.
- Percent-encoded Data URIs without Base64 are not supported. Incomplete data, invalid characters, or incorrect padding produce an error.
Privacy
All files are processed only in your browser and are never uploaded to a server.
File names, entered text, and results are processed only in your current browser. Your input is not saved automatically. Download any results you want to keep before clearing the tool or leaving the page.
FAQ
Is Base64 a compression format?
No. It represents binary bytes as copyable text. It does not compress files or automatically convert their formats.
Why is Base64 larger than the original file?
Every 3 original bytes usually become 4 Base64 characters, increasing the length by about one-third. Short inputs may include padding. A Data URI also adds a short type label.
Can I use any file type?
Yes, within the size limits. Images, PDFs, ZIPs, text, and other files can be encoded or decoded without being automatically opened or executed.
Are files uploaded?
All files are processed only in your browser and are never uploaded to a server.
How can I tell what type of file it is?
The tool uses signature bytes in the decoded content as a reference and also shows the Data URI or manually entered MIME type. An unknown format cannot be confirmed from its extension alone.
Can the input contain line breaks?
Yes. Valid whitespace and line breaks are removed before validation. Other invalid characters are not silently ignored.