What is Base64 encoding and why use it for files?

Base64 is a way of representing binary data (images, PDFs, fonts, archives) using only 64 printable ASCII characters. It lets you embed a file directly inside text-based formats such as HTML, CSS, JSON, XML, email (MIME) or a database column where raw bytes are not allowed. The trade-off is size: Base64 output is about 33% larger than the original file.

What is a data URL and when do I need the prefix?

A data URL looks like data:image/png;base64,iVBOR… It bundles the MIME type and the Base64 payload into a single string you can drop straight into an , a CSS background-image, or a JSON field. Tick "Include data: URL prefix" when you need that self-describing form; untick it if you only want the raw Base64 to store or transmit separately.

Is there a file size limit?

There is no hard limit, but everything runs in your browser tab using its memory. Files up to a few megabytes encode instantly. Very large files (tens of MB or more) can be slow or hit the browser memory ceiling, because both the file and its 33%-larger Base64 string must fit in RAM at once.

Are my files uploaded anywhere?

No. Encoding uses the browser FileReader API and decoding uses the built-in atob function, both 100% locally. Your file never leaves the device — there is no server, no network request and no analytics on the file contents. You can confirm this by disconnecting from the internet; the tool still works.

How do I decode Base64 back into the original file?

Switch to Base64 -> File, paste either the raw Base64 or a full data: URL, optionally type a file name, and click Decode & download. If you paste a data URL the tool reads the MIME type and picks the correct extension automatically; if you paste raw Base64 it defaults to a generic binary file, so add the extension yourself in the name box.

Why is my decoded file corrupted or "invalid Base64"?

The most common causes are truncated copy/paste (the string was cut off), stray whitespace or line breaks pasted from email, a missing data: prefix so the wrong MIME type is assumed, or padding characters (the trailing = signs) being stripped. Valid Base64 length is always a multiple of four; the tool flags input that fails this check before you download.

Base64 File Encoder & Decoder

A Base64 file converter that works in two directions, entirely inside your browser. In encode mode it turns any file — a PNG, JPEG, SVG, PDF, web font, JSON document or zip archive — into a Base64 string or a complete data: URL you can paste into HTML, CSS, JSON, an email template or a database field. In decode mode it takes a Base64 string (or a full data URL) and rebuilds the original bytes into a real file you can download. It is built for developers embedding small assets inline, support engineers reconstructing a file someone pasted into a ticket, and anyone who needs to move binary data through a text-only channel.

How it works

Encoding uses the browser’s FileReader API. When you drop or choose a file, the reader produces a data: URL — the MIME type plus the Base64 payload — which the tool splits so you can copy either the full data URL or just the raw Base64. A checkbox toggles the data: prefix on or off, and a live readout shows the original byte size, the detected MIME type and the exact character length of the output (always about 33% larger than the source, which is the cost of Base64).

Decoding reverses the process with the built-in atob function. Paste raw Base64 or a complete data URL: the tool strips any data:…;base64, prefix, validates that the remaining text is well-formed Base64 (length divisible by four, only the allowed alphabet and padding), converts it to a byte array, wraps it in a Blob with the right MIME type, and triggers a download. If the payload is an image it even renders an inline preview before you save. Every conversion you run is logged to a small history list in localStorage so you can see what you recently encoded or decoded — that history stays on your device and can be cleared with one click.

Example

Suppose you have a 12 KB PNG logo you want to inline in a single-file HTML email so it never breaks when the recipient’s mail client blocks remote images. Drop the PNG into the encoder, keep the data: prefix ticked, and copy the result — something like data:image/png;base64,iVBORw0KGgo…. Paste that straight into the src of an <img> tag and the image travels with the document.

Going the other way: a colleague pastes a long data:application/pdf;base64,JVBERi0… string into a chat. Switch to Base64 -> File, paste it in, type report as the name, and click decode — you get report.pdf back, byte-for-byte identical to the original, with the extension chosen automatically from the embedded MIME type.

Original file	Approx. Base64 length	data: URL prefix
12 KB PNG	~16,000 chars	`data:image/png;base64,`
48 KB PDF	~65,000 chars	`data:application/pdf;base64,`
2 KB SVG	~2,700 chars	`data:image/svg+xml;base64,`

Everything is computed locally in your browser — no file is ever uploaded, stored or transmitted.