What is the difference between the base64 string and the data URI?

The data URI is the full value, like data:image/png;base64,AAAA..., including the MIME type prefix. The base64 string is only the payload after the comma. Use the data URI for inline src/href attributes and the bare payload when an API expects just base64.

Why is the base64 larger than my original file?

Base64 encodes every 3 bytes as 4 ASCII characters, so the output is about 33% larger than the source. The tool shows the exact size overhead for your file.

Is my file uploaded anywhere?

No. Encoding uses the browser's FileReader and decoding uses atob, both running locally. Your file and its contents never leave your device.

Can I decode a full data URI, not just the payload?

Yes. If you paste a value starting with data:, the tool strips the prefix automatically before decoding. It also tolerates URL-safe base64 and whitespace.

What name does the decoded file get?

You choose the output file name before downloading. Because raw base64 carries no file name or extension, set the correct extension yourself (for example .png or .pdf) so your system opens it properly.

Base64 File Encoder / Decoder

Base64 is a way of representing binary data using only the 64 printable ASCII characters A–Z, a–z, 0–9, + and /. It lets you embed a file inside text-only contexts such as JSON payloads, HTML, CSS, or email. This free tool encodes a file to base64 and decodes base64 back to a file, all in your browser.

How it works

To encode, the tool reads your file with FileReader.readAsDataURL, which yields a string of the form data:<mime>;base64,<payload>. It splits off the payload so you can copy either the bare base64 or the full data URI. Encoding groups the file’s bytes three at a time and maps each group to four base64 characters, which is why the output is roughly 33% larger than the input.

To decode, the tool takes your pasted base64 (stripping a data: prefix if present), runs atob to recover the original bytes, packs them into a Uint8Array, and offers the result as a downloadable Blob.

Tips and notes

Base64 is an encoding, not encryption — anyone can decode it, so never treat it as a way to hide secrets. It is best for small assets; embedding a multi-megabyte file inline bloats your HTML or JSON and slows parsing. When decoding, remember to set the correct file extension yourself, because raw base64 does not record the original file name or type.