About this tool

Base64 to File

Turn Base64 strings or data URLs into downloadable files.

Base64 to File decodes a Base64 string or a data: URL back into the original bytes, identifies what the file actually is by reading its magic number, and saves it with the correct extension. It checks more than 30 signatures — PNG's 89 50 4E 47, JPEG's FF D8 FF, PDF's %PDF-, the ZIP local-file header PK\x03\x04 and others — so a payload with a wrong or missing MIME type is still saved correctly. It is for developers pulling attachments out of API responses, logs and database rows.

How to use Base64 to File

1. 1

   Open Base64 to File on AltFTool — it loads instantly in your browser.

2. 2

   Paste the payload into the Base64 payload or data URL box; the bytes are decoded in this tab and the type is read from the magic number, so there is no format to pick.

3. 3

   Check the Decoded payload panel — Detected type, MIME type, Decoded size, Base64 length, First 8 bytes, Byte-order mark, Entropy, Declared media type and Suggested file name, plus a Text preview of the first 240 characters when the payload is text.

4. 4

   Set a name in File name (extension is added for you), then click Save file to download it, Copy as data URL to copy the payload with its detected MIME type, or Reset to go back to the sample.

Why use Base64 to File

• Type from the bytes

  The extension comes from the file signature, not from the sender's Content-Type header.

• Mismatch warnings

  If the data: URL claims application/pdf but the bytes are a PNG, the tool says so.

• Entropy check

  A reading at or above 7.5 bits/byte tells you the payload is already compressed or encrypted.

Common use cases

• Recover an email attachment that survives only as a Base64 column in a database export
• Check whether an upload stored as Base64 is really a PDF, or an HTML error page that was encoded by mistake
• Turn a data: URL copied out of a browser devtools panel back into a file you can open locally

Frequently asked questions