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Convert any file to Base64 (or Data URL) and decode Base64 back into a downloadable file — all in your browser. No data is uploaded to a server.
Convert any file to Base64 (or Data URL) and decode Base64 back into a downloadable file — all in your browser. No data is uploaded to a server.
Nextooly’s File ↔ Base64 Converter is a versatile, developer-friendly tool that runs entirely in your browser. Drag and drop any file to generate Base64 or full data URLs, or paste Base64 text to decode it back into a downloadable file.
The tool detects file types using MIME hints and magic bytes, making it ideal for working with APIs, JSON payloads, embedded resources, and debugging binary data. Because everything happens locally, even large or sensitive files stay on your device—no uploads, no logging, and no external storage.
Example
Input: A File file or pasted file content you want to transform.
Output: A Base64 result you can download, copy, or reuse immediately.
If File to Base64 and Base64 to File is close but not quite the right fit, these related Nextooly tools cover adjacent developer & code workflows without sending you to another service.
Best if you need to compress multiple files into a ZIP archive or safely inspect and extract files from an existing ZIP — all inside your browser. Files are not uploaded to any server.
Best if you need to encode and decode Base64 safely in your browser.
Best if you need to encode or decode URL components safely.
Does this tool upload my files or Base64 data to any server?
No. All encoding and decoding happens entirely inside your browser. Your files, Base64 output, previews, and decoded downloads never leave your device and are not stored anywhere.
Why is the Base64 output much larger than the original file?
Base64 encoding increases file size by about 33%. This is normal because binary data is converted into text using a 4:3 expansion ratio. Very large files will produce extremely long Base64 strings.
Can I convert any file type to Base64?
Yes. Any file can be converted. The tool reads the file as a Data URL, extracts the MIME type, and generates Base64 text. Images, PDFs, ZIP files, videos, and all other formats are supported.
How does the tool detect file type when decoding Base64?
The tool uses magic-byte analysis on the decoded bytes to identify common formats such as PNG, JPG, GIF, PDF, ZIP, and MP4. If no known signature is found, it falls back to the MIME type in the data URL or defaults to application/octet-stream.
What is the difference between Base64 only and Data URL output?
Base64 only provides the raw Base64 string, ideal for APIs, JSON, and compact storage. Data URL includes the full prefix `data:<mime>;base64,...` which is useful for embedding images or files directly into HTML, CSS, or documents.
Why does decoding large Base64 sometimes warn that the browser may freeze?
Extremely large Base64 strings require heavy memory and string processing. Browsers may slow down, freeze, or crash. The tool warns you if the input exceeds 15 million characters so you can avoid accidental decode attempts.
Can I decode a Base64 string that is a full data URL?
Yes. The tool automatically detects data URLs such as `data:image/png;base64,...` and extracts the MIME and Base64 payload before decoding.
What happens if the Base64 text contains invalid characters?
The tool validates the characters and will show an error if the input contains anything outside A–Z, a–z, 0–9, +, /, =. Invalid or incomplete Base64 strings cannot be decoded.
Why does the decoded file automatically download?
After decoding Base64 into binary, the tool creates a Blob URL and triggers an automatic download with a safe filename. If no extension is provided, the tool attempts to infer one from the detected file type.
2026-03-10
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